é Panes i se | ISSN 0265-2919
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36
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4
IRS.1.15 Aus $2.15 NZ $2.65 SA R2.45 Sing $4.50
- events. One program calculates the amoun
THE ARM’S BUILD-UP Having given the
ACTS ON FILE The use of databases in education not only provides children with access to large bodies of information, but
also allows them to develop useful skills in manipulating data
BUSINESS ON A BUDGET Claimed to be IBM-compatible and capable of running MS-DOS based software, the Sanyo MBC- 550 could be considered a real bargain for business users. We take a look inside
NAMING NAMES When setting up a database of information, it is essential that the designer has clear expectations of what sort of data will be entered and how this will be used. We look at a basic specification
ON THE SET We take a look at PASCAL’s use of sets, discuss the order of precedence of set operators, and develop games of bingo and snooker using these data structures
FROM MONITOR TO MOUSE A weekly glossary of computing terms
ANCHORS A WEIGH The module we develop this week in our simulation game consists of those parts of the program that
report on the weekly progress of the voyage
LAST CALL We conclude our discussion of the BBC Micro’s OS by considering three machine code routines that make use of
of unused memory
pattern cutouts for the base and arm sections of our robot arm in the previous instalment, - we now give instructions showing how the components are assembled
COVER PHOTOGRAPHY BY MARCUS WILSON — SMITH ;
EDUCATION APPLICATION
los Oh
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e information
TSE,
Type YES or NOYES
You can
see all the DINOSAURS see one DINOSAUR
ask something else
go back to Choice Page
Press A, B, CorD 6 C_
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nit = jeader m nthe fe id ‘ol country, the
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| children heard hae banxite miners had- gone on strike in Surinam | they could quickly discover the
alae | for understand — frei = ee of . sl ihe : qu estions es and a5 properly ao organising = th eir “input = Those rents ~ who, eter aft er : experiencing - : i database, enter higher education and eventually > ‘the workforce, au surely possess 2 an eee
have seen how databases can manipulate large bodies of related data given the fundamentals of proper structuring. In our second instalment on databases, we will construct a simple system based on the idea of an address book, highlighting the importance of careful planning in the design stage.
LE a
fa i iit E sea is i ret
One of the major advantages of an old-fashioned address book is that very little structure is imposed beyond basic alphabetic ordering. It is flexible in the sense that you can have entries such as:
PETER GLOVER, 16 Rhiwbinal Cresent, Cardiff (0222-601227) — his girlfriend’s called Clair — office: 0222 680545 Ext 160 — call after 4 — moves to new flat in Jan.
Followed by: GODFREY — 696-1949 Followed by: GREG — see Ashton-Tate
Using an address book, you are free to list people under their first names, their surnames or even by ‘indirect addressing’ with ‘pointers’ to other entries. As soon as a database such as this gets transferred to a computer, however, a more systematic approach is usually called for. - Given that a computerised address book has some disadvantages compared with the original, let’s design a format for one that will be flexible enough to cater for most circumstances. We'll consider each field in turn, starting with the name.
Names come in two parts: the generic half, called the surname, and the specific half, called the forename. In most countries, the forename(s) are followed by the surname, whereas in China, Japan, Hungary and some other countries, the surname precedes the forename. In Japan, there is only ever a single forename (except that it follows the surname), while in a Chinese community in England, it is customary to have an English forename as well as a Chinese forename. Thus, Li (surname) Yu Chow (forenames) will be known to most of his English friends as Paul.
Already, we have plenty of opportunity for confusion, and we're only considering the name field. Clearly, we will have to impose some discipline, and decide whether forenames or surnames are to come first, and how long an ‘allowable’ name may be. Names may be as short as Ng or aslongas Cholmondley-Smythe, possibly
1104 THE HOME COMPUTER ADVANCED COURSE
NAMING NAMES
even shorter or longer, so we must always allow for extreme examples. If the database manager (DBM) uses fixed length fields, we will have to choose a field length more than adequate for the longest name we are likely to encounter. (The disadvantages of fixed length fields will be discussed later in the series.)
If we have to impose a format, as indeed we do when designing a database, it is probably simplest to use the surname field as the primary key field, so we will start with the surname and follow it with one or more forenames. The address also poses
problems. Doubtless, you have seen clip-out
forms in American magazines that ask for your City, State and Zip Code. British addresses simply don’t fit into that format. A further complication arises when you consider that even the ‘Name, House Number, Street, City, County, Country’ format is not always appropriate. In Japan, for example, the city is listed first in an address, followed by the district within the city, followed by the lot number of the building plot within the district, with the addressee’s name coming last. »
A BASIC SPECIFICATION
In this simple database example, as in more complex ones, it is probably not possible to cater for every conceivable combination, so we will have to settle for a compromise. Assuming you are never likely to be communicating with someone having 16 forenames, let’s see how well the following basic skeleton would work:
@Surname Field — up to 40 characters @Forename Field — up to 60 characters
@ Address Field 1st Line — up to 80 characters @ Address Field 2nd Line — up to 80 characters @ Address Field 3rd Line — up to 80 characters @ Address Field 4th Line — up to 80 characters @ Address Field 5th Line — up to 80 characters @ Telephone Field — up to 20 characters
®@ Note Field — up to 80 characters
This basic specification should cover most eventualities, though there may still be problems. One potential difficulty is the limited length of the Note field. Another problem is that Country is not specified as a separate field. Depending on the length of the address, the country could be found in the third, fourth or fifth address fields, or not at all. This would not normally be a problem until we wanted to search our database using Country as a key. If your database application had to deal with many foreign correspondents, it might be better to design the database with a separate Country field. Decisions such as these will always be needed at the design stage.
The DBM you run on your computer will determine the ease with which you can implement a specific database on your system. One of the very simplest DBMs is Caxton’s Card Box. The program has limited facilities for extracting and manipulating data, but if your requirements are straightforward, it will give you the results you need with the minimum of fuss. Card Box does not give you a sophisticated programming language to manipulate fields or records. It does, however, allow you to extract specific records by entering simple commands at the keyboard. Using Card Box to create the database outlined above, you need only to load the program and follow a simple sequence of entries.
USING CARD BOX
The first thing you have to dois decide on a format for the record. This format determines what information will be stored, how it will be indexed (that is, which fields will be designated as ‘key’ fields) and how the records will actually appear on the computer screen or printouts. If we call the database file ADBOOK, Card Box will create a format file called ADBOOK.FMT. This can be edited if required to alter the way the information is displayed. Alternative format files can also be created to display the database information in different ways.
As with most DBMs Card Box allows you to enter ‘permanent’ text in each of the fields. In the case of an address book, it is pretty obvious what the significance of each field is: John Smith is clearly a name and not part of an address¢ similarly, 0222-680545 is obviously a telephofe number. In other databases, you might need to be reminded what the significance of each figid 1s. This is where ‘permanent’ text comes inflandgy. Compare these two records:
06116 3995 86 34.75 Dongle with widget nozzle
and MAKER’S PART NUMBER volo OUR PART NUMBER cole NUMBER LEFT IN STOG ce PRICE Oe DESCRIPTION Dong vce oe
The informationds identical in both cases, but the second examplé, with permanent text that appears in every record, makes mistakes much less likely.
Card Box allows each field to be given one of four possible indexing attributes: NONE, MAN(ual), AUTO or ALL. In a stock database, it is unlikely that we would ever need to use PRICE as a Key field; you are not likely to ask: “Do you have any parts that costless than £40 and more than £307?’ It is quite possible, however, that we would need to know how many #06116 items are still in stock, so that
MAKER’S PART NUMBER would need to be made 4 key field.
Returning to our address book example, ware sure to want to search the database by Namg, and probably by Forename too. Both of these’ would need to be made key fields. If we were maining a business, we might also need to search 4ecords Dy City and possibly even by telephone area dialling code. It is important to remember that you Cannot create an efficient database until you have worked out how you are going to use it. Unlike the old card indexes, databases require that you anticipate beforehand how you are likely t6 use them.
Design Elements
Megafinder allows you to degign your Own Toms. This one was derived from@ne Same 1orm, Supplied ready-made with the program, used in Our Oiner screen display
Business Card File
Company?
Address:
Gets: D Phone:
Keywords:
Comments: L
Layout: {mark fields with ".", CTRL-B ins. ae, CTRL-N del.
line, CTRL-C¥3
COMMAND LINE
1)1S Shows Some O1 ine commands thal may be used When ediing 2 desig) Lines
and Chalaciers ay De inceriec and deleted, and tne (nisied design Can be Saved 10 disk Dy pressing UIRL-U
Company: Home Computer Advanced Course Address: 14 Rathbone Place Town : LONDON Code:W1P 1DE Telephone:@1 631 14393
Contact:STEPHEN COOKE \STEVE MALONE
Keywords: PUB * WEEKLY * 1.68
Product received:Subscription
Actions: 25/5/85 renew sub
Find: lindex 1 = ACD Deelete Ptrint Qtuit
Meatch = OFF ¢arrows> Jtump Cthange
FIELD LENGTH
These are indicated by underjine CharecierS(_) |e tdi lengin Ol all he fields in a ionn determines 10W many (01s May be Siored in a iile. Thereiore, | makes sense io Keep eds 4S 501 ass practical, Dealing in mind ihe nature of (he dala inal will be eniered
FIELD LABELS These are entered Dy ine user when designing ie (orn and 0 1S Dr0dT al), ale enlirely (01 ine user s convenience. (fe program uses iiem) wien displaying lormation on ive Screen Dut takes 10 account Oo! field iabels when sorting dala, whicn iL coes using FIELD IDENTIFIERS
FIELD IDENTIFIERS
Nol io be coniused wilh ie FieLD LABELS, ne identiiers celery ine fe order in which fields will be accessed wien entering iniormation. Identifiers also enable fields to be Soried Separalely oF in groups. Using Megalinder 5 INDEX Option, allocating (eld U io Index | would allow te user 10 Sort Quickly through ine different records according to ine alphabetical arrangement ol cies
Allow Us To Show You Our Card
Database management Systems nay offer several different methods of manipulating information. This screen dump of Megafinder, a DBM running on the Apple computer, shows a selected record from atilenamed Business Cara and, below this, alist of command options. Data held by the program can De
sorted into up to tour different INDEXes to speed information recovery. [he DBI will also search for a AICH between input data and stored data, JUMP to Specified sections of the database (€.9. to the section holding company names Starting with IM), CHANGE and DELETE information, and PRINI a record or report, either to the screen or a printer
THE HOME COMPUIER ADVANCED COURSE L105
veonononseganenenecanannanssnnse
_At the start of the journey, each crew member's strength is set at 100 in the array TS(,). The
a makes a weekly. calculation to check it far and the money remaining. The accumulated zg
at line 800, and is increased by the weekly wage |
|
ANCHORS
Having everything we need to se New World in our tradi } we can lift anchor,
gggeetten,
there are sufficient stocks of each provision to last the journey. If supplies ofa particular type run low, the player is asked if the crew should go onto half
be issued for one week and would reduce the crew.
. pena by five units.
If one type of supply becomes: mie: each ctew member’s strengthi 1s reduced by 10 for every ~ week they are without it. For example, should the Serew run out. of fruit and: be on\half rations of water, their weekly strength rating would decrease. ae 15; if the water ran out ——- ine pein
a
issued at the Sau of the next eck ae ee et The health of the crew is given. at th Ae = pesmi ~
of each week by the subroutine at line 4000.-There ~
are five classes of health, which are determined. by strength rating. The highest classification is very.
healthy (strength rating 75 — 100), followed by healthy (50 — 75), sick (25 — 50) and very sick (1 - 25). When the strength rating reaches 0, the crew member dies and is buried at sea, but the wages of the deceased are still accounted for each week and paid to the next of kin when the ship returns to port. This subroutine also gives the wage bill for
1106 THE HOME COMPUTER ADVANCED COURSE
eter can be | tes hae
: “weeks,
AWEIGH
the coming , week, the total wages for the voyage Som
wage total is reset to zero at the start of this section,
bill each time through the loop. If the bill becomes | ~~rations of that provision: ‘The half rations will only: ~Jarger than the balance of gold (as checked bythe.
subroutine at line 5000), the player is warned that _
\a trading profit will be needed to pay the crew.
If all goes well, the voyage should take eight but ‘unforeseen circumstances “could increase. the value. Line 801 creates a string variable, ‘HS, to\ indicate if the crew are on half
%,
rations. The routine determines the- strength and—.
_type of each crew member by checking the type/ —_ — TS(, ) L sets ab a ot at line 4060
t
|
i
program Sat to line At i0. if there’ iS eon se
the « crew. aie in a anray, fe 4075; prints the
must be ecole in the yan s log
strength rating indicates death, each empty section on the array would appear to represent a dead crew member. To avoid this problem, it is reset to -999 for one week when a rating reaches 0. At the
i i j so
4 Hy
a ee Sn a a a ee ee pn aae
PA(), is greater than zero. If this is not the case then the strength of each crew member is reduced by a factor of 10. This reduction is actually handled by a small subroutine at line 9300 that reduces the strength rating of each crew member by the value
of WF. This subroutine can therefore be used to reduce the crew strength by differing amounts. We : <so...need only to set WF to the desired value before ae ~ calling: -the subroutine. Si SS ge == =* Ee the amount of ea remaining 1S greater
a
Nateat orovision | ~yoyag e. ate ao is calculated: mM. line 5180
age
the voyag : tt oc,
Nis given the’ ‘option.of placing ‘the crew on half _Tations. ‘of that.particular.type-of provision.
status of each provision type (whether on half or
= iS ie ae the projected requirements, the: player. :
} aa i oe Da
A full \ ano) is indicated by \the array HR() a = \ DIMensioned at line'802. When on full rations the. \ a —- “ts ‘array 6 eitientiis set tot ifth e particular provision ° a <= : “Cis reduced to half then the c responding airay \ : , “oo élement jis set to 0.5. If the crew is on half rations . . s aS See =e thesubroutine at line 9300 \— | \\ _ the strength rating of each crew membet by five, \ | : Ss The final check made\by this\ routine before, \ ‘ | = uing the ration i s to see if the amount of the | He: — oS Se a eee vision remainin; is less than the amount to be \ ar ed. If this is the case, then only the amount | aining is issued and, to indicate that no — | | visions. are left, the corresponding element Of .)....00c0.0c cfm et | h provision array is set to -999. | end of the week it is set back to 0 and the roar | | / | informs of the death at the start of the next wee Ss a= ~ Re-setting it — it to ae that ‘rating == — = 4 panne the following weeks. This anetet a j / | i record of dead crew members at the start of each / / / Clo oo of rageate eth pee is. =e =. = checked by lines 4080 to 4098. Their rati 2 - | ‘matched against the four states of health, an fine / 7 a 4099 vil print the state of each. The strength/ = Ss hc ~~ type loop ends at 4110, which sends the program . ys Ss ' back to look at the next section of/the aryay. / J x | The weekly wage bill iS calculated usin another ae we = : --loop between lines 4120-and-4135, and uused-once- oS eS | _ for each of the five crew types. Wages for each type —_—— = | are calculated by the/ equation at line / / oe — Tamil multiplying the count, for each type by the wa |
ew, | See we a ree eek Aer ely A
rate, and accumulating it/in the variable, iW.
Created and set to 0 at the start of each week by ' tine 4119, WW represents ‘the weekly wage, printed. Sale tine 4145. Ttis — to the <— for. the
a ; for ‘each mon a several | checks a are made on the level of rations remaining. The first of these is a check to ensure that some rations remain. This can be tested by simply checking that the amount of the provision, held in
THE HOME COMPUTER ADVANCED COURSE 1107
ERRATUM In the listing of our adventure game Digitaya, on page 1020,
BBC Micro users should
change all occurrences of the variable names LNS() to LS() and LN toL
PROGRAMMING PROJECTS /SIMULATION GAME
Module Four: The Voyage 25 scent 0 ul e ou a y g 42325 PRINTOAC1)::S¢="BOTTLES OF MEDICINE*":GOSUBS1
a
Length Of Voyage Variable 423 GOSUBS2a0
: 4332 IFOAC2) =@THENS342 40 oe reN Dee ee 4325 PRINTOAC2): :SS="GUNS*" :GOSUB9S100 43460 GOSUBS268
4 4342 IFOA‘3)=Q@THENS352 Main Voyage Loop 4345 PRINTOA(3)::S$="BAGS DOF SALT*":GOSUBS100 800 WT=0 4350 GCSUBS2eaa @@Q1 HS="N" +REM HALF RATIGN INOICATOR 4352 IFOA(4)=0THENS362 @O2 DIMHR(4):!HR(1)=1SHR(2)=13HR(Z)=11HR64)=1 94355 PRINTOAC4)::S#="BALES OF CLOTH*":GOSUBS100 820 FORWK=1TOJL + REM MAIN VOYAGE LOOP 43660 GOSUBS200 S25 GOSUB49@@a: REM CREW STATUS REPORT $362 IFOACS)=@THENS3S 72 830 GOSUB4200:REM PROVISIONS REPORT 4365 PRINTON(5): 'S#="KNIVES*":GOSUBS100 835 GOSUB4300:REM OTHER GOODS REPORT 4370 GOSUBS200 a 840 GOSUBS2O0:F 2 INTCHRS¢ 147 > 4372 IFOAC6)=OTHENS388 Sde PRINT: PRINT*PRINT 4375 PRINTOAC6)? ':S#="JEWELS*" :GOSUBS100 843 S$="I1T IS ESTIMATED THAT THE VOYAGE *":GOSUBSIO 94380 GOSUBS200:PRINT a 4382 PRINT"YOQU HAVE"; #:S$=" GOLD PIECES LEFT*":G 844 PRINT"WILL TAKE A FURTHER": JL-WK +1: "WEEKS" OSUBS 108 L 845 GOSUBS208 4384 GOSUBS20a @46 PRINT: S#=K#!GOSUB9S100 4397 PRINT: S#=K#$:GOSUB9100 e447 GETIS: IF 1#=""THENS47 9398 GETI#: IF I$=""THEN4398 850 GOSUB5S@@@:REM CHECK WAGE BILL 4399 RETURN
S55 GOSUB5190: REM ISSUE RATIONS 889 NEXT WK
Wage Bill Subroutine Crew Status Report 5@@@ REM CHECK WAGE BILL
50@5 IFWT>MOTHENSO10 4ag@ REM CREW STATUS REPORT 5aa@g GoatTosa99 4010 PRINTCHRS( 1473) S@1i¢i PRINTCHR$(147) 4@20 St=" CAPTAINS LOG*":GOQSUB910@0 5020 PRINT:PRINT!IPRINT 4025 st-" =: ";GOSUBS 106 5@25 St="THE CREW HAVE HEARD A RUMOUR*":GOSUBS100 4030 GOSUBSeaa 5038 S#="THAT YOU DON'T HAVE ENOQUGH*" :GOSUB9160 4035 PRINT"AT THE START OF WEEK": Wik 5035 S#="GOLD TO PAY THEM AT THE ENDx*":GOSUBS100 4040 SH="THE STATE OF THE CREW I[S:x" '+GOSUBS 100 5040 S$="OF THE VOYAGE. *":GOSUB9100 4045 GOSUBS2AMa:PRINT : 5045 GOSUBS2ZQ0:PRINT 4055 PRINT SAQS5SQ S$="THEY ARE GETTING ANGRY !!%*":GOSUB9S100 4@60 FORT=1TO16 5055 GOSURS200:PRINT 4070 IFTS(T,1)=O8THENS110 5Q@6Q@ S#t="LET'S HOPE YOU MANAGE TO MAKE*":GOSUB9S10@ 4@75 PRINTC#(TS(T,-1)39:" cP: 4078 IFTS(T,2)=-S999STHENSS="DEAD !1!!11!11)2*":GOTO489 GAGS St="A TRADING PROFIT! *"!:GOSUB91O09 g 5066 GOSUBS20a8 4Q@2Q IFTS(T,2) >75THENS#="VERY HEALTHY) *":GOTQ4099 SATA PRINT: S$$=K$:GOSUBS100 4085 IFTS(T,2) >SOTHENSS="HEALTHY?*":GOTOS8033 5@e0 GETI$: IF1$=""THENSOSa 4a95 IFTS(T,2)>2S5THENSH="SICK | >*x":GOTQ4a9qa 5999 RETLRN 4098 St="VERY SICK |! >" 4a99 GOSUBS100:GOSURS2a0a0 : : 411@ NEXT T issue Rations Subroutine
att) Goebevede re 5106 REM ISSUE RATIONS
5103 PRINTCHRS#( 147)
8 5105 S#=" ISSUING RATIONS*":GOSUB9100 Weekly Wage Bill 51Q6 S#s=" as ee Se x": GOSUBS9100 4118 WhW-6 5107 GOSUBS2Q@:PRINT"WEEK "? WK: PRINT 4120 FORT=1TQ5 : 5108 Hp="N" : 4130 khl=WW+ (CO CT *eWG(T)? S110 FORT-1TO4 4135 NEXT 5112 HR¢T)=1 4140 S#$="WWAGE BILL FOR THE WEEK*"” 'GOSUBS100 5115 IFPACT) >@THENS180 4145 PRINTWW: "GOLD PIECES" 5126 PRINT"NO ":P#C(T):" LEFT! !)!":GOSUB9200 415@ GOSuBSs2eaa 513@ S#="THE CREW IS GETTING WEAKER !!*":GOSUBS91@0 4155 WT=WT+h 416@ S#="TOTAL WAGES FOR VOYAGE SO FAR: *":GOSUBS1@ 5125 WE=109:GOSUB93a0 a 5139 GoTaseasa 4165 PRINTHWT: "GOLD PIECES" 5180 *=(PNCT) eCNd*¢(JIL—-WK+I> 4170 GOSUBS2H90 5185 IFPACT)<XTHENS2o0a 4175 PRINT"MOGNEY LEFT = ":MO: "GOLD PIECES" 5190 GOTOSe272a 418@ PRINT:S$=K#! GOSUBS 100 5200 PRINT"RUNNING SHORT OF ":P$¢T) d18a@Q GETI#: IF IS=""THENG19G 5205 GoOSuURS2zaa 4199 RETURN 5210 S#="00 YOU WANT TO PUT THE CREW ONx":GOSUB910 a ; _. 5215 PRINT"HALF RATIONS OF ":P#(T) , Provisions Report 5220 INPUTI$: I$=LEFTS(I#, 1) a2an REM PROVISIONS REPORT 5221 IF 1#<¢>"Y"ANDO I1$<>"N" THEN 5220:REM INPUT ERR 4205 PRINTCHRS( 147) OR . 4206 PRINT"AT THE START OF WEEK": bK:GOSUBS2aa see> iF ie Yee ee 5 4210 S#="YOU HAVE THE FOLLOWING«*":GOSUB9190 Se3@ HR¢T)=.5tHe="¥ 4215 S#="PROVISIONS LEFT: *":GOSUBS1aa sere eee gee be nt eocueseon 5250 S$="THE CREW IS GETTING WEAKER! «":GOSUB9100
SerO X=PNCTI *HRCT)*CN Sere IFX>PACT) THENK=PACT >?
4225 FORT=1T04 4226 IFPACT)=Q@QRPACT>=-S99THENS240
4230 PRINTPACT):US(T):"S OF ":P#(T) pers FAC TORPACTO
4232 K=INTCPACT)/CCNEPNCT))) 5e80@ IFPA‘CT)=@THENPA‘CT)=-399
4235 PRINT" (ENOUGH FOR":%:" WEEKS)" 5285 PRINTX:US(T):"S OF ":P$(T):" ISSUED" 4239 GOSUBS2aa 5290 PRINT: GOSUB920@: NEXT
424@ NEXT 5295 PRINT: S$=K#:GOSUB910@
-42930 PRINT:S#=K#:GOSUB91@0 S298 GETI#: IF 1$=""THENS298
4295 GETI#$:! IF 1S=""THEN4295 S233 RETURN
4299 RETURN
Reducing Crew Strength Other Goods Report 9300 REM REDUCE CREW STRENGTHS BY WF 42@@ REM OTHER GOODS REPORT | 9310 FORS1=1T016 43@5 PRINTCHRS( 147) 9320 TS(S1,2)=TS(S1,2)-WF 436 PRINT"AT THE START OF WEEK "+ Wk !GOSUB9200 9330 IFTS(S1,2)<1THENTS(S1,2)=-999 4310 $$="YOU ALSO HAVE: x":GOSUB9 10a 92408 NEXT 4320 PRINT: GOSUB920a 9399 RETURN
1108 THE HOME COMPUTER ADVANCED COURSE
BUSINESS ON A
BUDGET
IBM PC under £1,000, the Sanyo MBC-550 represents a less expensive addition to the 16-bit Intel 8088-based computer market. But hardware restrictions and a lack of specifically designed software, at least for the present, limit this otherwise sensibly produced machine.
Despite rapidly falling prices of 16-bit processors, most computers based around 16-bit technology, apart from the Sinclair QL, are still very expensive. It is hard to understand why this is. Sinclair Research had proved that it is possible to produce a 16-bit machine profitably for under £400, yet most comparable micros are well into the four- figure range. The reason probably lies with the type of customer who is in the market for such a machine. These tend to be business users whom manufacturers seem to believe can afford to pay a bit extra. This appears to be particularly true of computers based around the Intel 8088 series of processors and is probably linked to the sales policy of the market leader, IBM.
With the standard IBM PC including a single disk drive costing around £2,000, most manufacturers building 8088-based micros consider that by shaving a few hundred pounds off this price, their customers will regard that as a bargain. But this still leaves a section of the market that cannot quite afford many of these, although still requiring a computer for business use. Until recently, this area of the market was occupied by business computers based around the Z80 processor that were equipped with disk drives enabling them to run CP/M. However, many manufacturers are now realising the potential of this neglected area of the business market, and are endeavouring to produce inexpensive 8088-based machines.
The Sanyo MBC-550 is one of the first of these to arrive on the market. Although Sanyo does not claim it to be compatible with the IBM PC, the MBC-550 does run the de facto standard MS- DOS disk filing system. ‘The machine is available in either a single or twin disk version and sells for around £1,000.
Like most business machines, the MBC-550 has two separate units, comprising the keyboard and the main computer. These are sturdily cased in a combination of metal and plastic, finished in a metallic silver. The keyboard is divided into three sections. On the far left are five programmable function keys which, when used in conjunction with the Shift key, produce a maximum of 10
functions that vary according to which application is currently in use. In Basic, these keys can be used as single keyword entries with commonly used commands such as LIST, LOAD and RUN.
The typewriter keyboard is well laid out with all the control keys in their usual positions. The control keys include a destructive Backspace and an Insert/Delete key, only one of which is operational in each application. There is also a very large Return Key, four times the size of one of the normal keys. On the nght-hand side of the Space bar is a Graphics key, which produces graphics characters on the screen when locked. On the far right-hand side of the keyboard is a numeric keypad that can be used as a calculator, or, if the Number Lock key is pressed, as a cursor control to enable full screen editing in BASIC.
The computer itself is a large flat box about the size of a video recorder, that has been made large enough to accommodate the optional Sanyo
monitor. Like the keyboard, it is mostly manufactured of sheet metal. On the front of the computer is the power switch and space for two disk drives, although our illustration shows the single drive model. The drives used by the MBC- 550 are of the standard 5zin floppy disk variety. On the front of each drive is a clip to hold the disk in position and prevent it from being removed while the drive head is reading it.
Sibling Differences
The Sanyo MBC-550 is a budget
priced 16-bit business machine which runs under the popular MS-DOS operating system.
. There are two versions of the
machine: the MBC-550 is the single drive version and the dual drive configuration is known as the MBC-555. The monitor shown here is not included in
the basic price of around £1,000
CHRIS STEVENS
THE HOME COMPUTER ADVANCED COURSE 1109
Bi a
CE
PERIPHERAL INTERFACES
The rear of the computer contains the power supply and the peripheral interfaces. Looking at the back of the computer, on the left side, you will see the power cable, the fuse housing and the earth connection. On the right, there is a Centronics parallel interface that will accommodate the connecting of a printer. A pair of monitor sockets [| = = are to the right of this. The first isan RGB socket, [| enabling the computer to run a colour monitor, [= while the other is a composite video jack that plugs | into the Sanyo green monochrome monitor. Above these interfaces are further expansion ports provided to accommodate extra peripheral interfaces at a later date.
The Line port above the printer interface is included for the connection of an RS232C serial interface that would facilitate the computer communicating with other computers, via a modem, or with any other serial device, such as a printer. Next to that is a port in which an MBC
7 series or Apple-compatible joystick interface [= = = = = could be fitted. This not only allowsajoysticktobe | Srinterinterlace fitted but would also enable the computer to be | Thisponaliowsany — controlled from a trackball, paddle or other | GeMlonics compatible paralie) external device. There is also an external bus —'[ se socket allowing other peripheral devices to be | 3 interfaced.
Unlike many manufacturers who object strongly to users tampering with their machines, Sanyo has thoughtfully included, in the user manual, instructions for the fitting of all of these peripheral interfaces, extra banks of RAM and a second disk drive if only one is currently fitted. | 0 This is a very welcome inclusion, although the | Perinieral itertace Gi — guide does mention that users should consult a | co ee LD qualified engineer if they are at all uncertain. The |~ ee tothe computer rest of the user manual is equally helpful. It | = = = = = contains a glossary of computer terms, a full
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tutorial description of Sanyo BAsic — including instructions on using the disk system from BASIC — and a wealth of technical information.
Sanyo BASIC, a derivative of Microsoft’s version, is certainly adequate, although it seems to be somewhat slow in_ processing arithmetical functions. The 8088 chip has long been noted as being sluggish when processing maths (hence the popularity of the 8087 maths co-processor), but the MBC still seems noticeably slower than most other 8088-based machines. Similarly, line drawing on the MBC-550 is also very slow. This is because Sanyo BAsic lacks a DRAW command, requiring line drawing to be performed by the PSET command, which simply turns on one specified pixel to a particular colour. Thus, drawing a line involves using a loop.
Apart from standard Microsoft-type commands such as MIDS, LLIST and CIRCLE, there are also commands to define and view windows on the screen. Structured programming is encouraged by the inclusion of the WHILE. .WEND conditional statement. Many Sanyo BASIC keywords can be entered by two or three keystrokes based around the Control key. For example, the keyword DIM can be entered by pressing CTRL, SHIFT and D simultaneously, while PRINT is entered by pressing CTRL and P. Although any move towards the simpler entry of BASIC keywords is to be welcomed, and many of the shortened keypress commands bear a relationship to the originals, it is difficult to imagine anyone attempting to remember the 40 commands available to write BAsic programs. More likely, they would attempt to memorise a few of the more commonly used shorthand versions.
Bundled with the Sanyo MBC-550 is an MS- DOS system disk, which also contains the Sanyo BASIC, the widely used WordStar word processing package and the CalcStar spreadsheet. Accompanying these packages is a manual giving full descriptions on how to use them. ,
One would expect the standard MBC-550 — based around the 8088 chip and running under MS-DOS — to have little problem running the vast amount of IBM PC software that is available. But the fact is that hardware restrictions within the machine meant that none of the IBM-compatible packages that we tested on the computer would run.
There is undoubtedly a market for low-priced MS-DOS business machines able to run IBM- compatible software. The question is not whether they will appear, but when. The Sanyo MBC-550 is a first attempt to break the £1,000 barrier, but unfortunately its lack of compatibility means that it will remain isolated. For the small business owner who only needs a computer to run competent word processing and spreadsheet facilities, the MBC-550 seems to be good value. However, anyone wishing to gain access to a wider software base than is available for the Sanyo will have to reconcile themselves to either spending quite a bit more, or else waiting a little longer.
THE HOME COMPUTER ADVANCED COURSE 1111
LOWER BASE
EXPANDED VIEW
UPPER BASE
FLANGED BALL-RACE
STEEL DOWEL
SIDE ELEVATION
6mm BRASS TUBING
6mm BRASS TUBING
THE ARMS BUILD-UP
6mm CROSS PIECE
_ 6mm CROSS PIECE
| SIDE PIECE LOWER BASE
SPACER
1112 THE HOME COMPUTER ADVANCED COURSE
After listing the necessary parts for our Workshop robot in_ the previous instalments, we can now _ begin its construction. Here we assemble the main body, the upper and lower arm sections, as well as make the elbow and shoulder joints using the previously cut out parts.
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THE HOME COMPUTER ADVANCED COURSE 1113
MAINBODY SIDEPIECE
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KEVIN JONES
In addition to pascav’s familiar data structures, such as arrays and files, the language also includes sets and records. We examine the first of these structured types, as well as summarising the levels of precedence for the PASCAL operators we have examined so far.
We often talk about a computer’s character set. But what precisely is meant by a set and how does it differ from an array? The main characteristic ofa set is that it is a collection of objects that can be processed as a single entity, rather than each element having to be accessed individually. A practical example would be the set of all people who program in PASCAL, or the letters of the alphabet that are vowels. There is often no particular ordering involved, with the only
question of interest being: is this particular object a _ member of the set or not?
_ For reasons of efficient implementation, PASCAL places some restrictions on sets. They can only have simple scalar types as their members — not arrays or other structured data — and there will be an (implementation-defined) upper limit on the range allowed for this “base’ type. The syntax is straightforward, for example:
TYPE Numbers =SET OFO. .127; Alphabet =SETOF‘A’.. ‘2’; ColourMix = SET OF ( Red, Green, Blue ):
The range of possible values of the ordinal base type of the set may be expressed with the same syntax as for subrange types.
Set variables are declared in the VAR declaration part, in exactly the same way as all variables in PASCAL, and may appear in statements literally (i.e: as ‘literals’) enclosed within square brackets, thus:
VAR codes : Numbers; palette : ColourMix; BEGIN codes :=[0.. 2, 4, 8, 16, 32, 64 ]: palette := [Red . . Blue ]; { etc. }
This segment would initialise the set codes to contain only the numbers 0 to 2 inclusive and 4, 8 and so on, as listed. Because there is no inherent order in the set itself (as opposed to its base type), we could equally well express this set as [64, 32, 16, 8, 4, 0..2] but notice that the subrange 2. . 0 (illegal in an actual subrange definition) would merely indicate an empty range. In fact, any set can be initialised to an empty set of its type with the
1114 THE HOME COMPUTER ADVANCED COURSE
statement: AnySet :=| ], which gives rise to the only exception to the general rule in pascAL, namely, the type of any literal is known by inspection. Without at least one member of the set appearing literally, neither we nor the compiler can determine its type. Fortunately, the empty set can only occur in assignments (as in the example) or expressions in which the other identifiers will have already had their types declared. This does mean, however, that the empty set is a subset of every set
- type, but that’s only natural.
SET OPERATORS
One of the most useful operators PASCAL provides
for set structures is, iike DIV and MOD, a reserved word: IN. It enables us to test for membership of a set, and is a relational operator that takes two operands. The left-hand side must be an expression evaluating to one of the possible members of the set — in other words, a value of the set’s base type — and the right-hand side may be a set variable or set literal. ‘The whole expression will give a Boolean result — true if the value is a member of the set and false otherwise.
So: N IN codes and Green IN palette are legal
Boolean expressions. The usual test for a character
being a digit could be written as:
IF (c >= ‘0’ ) AND (c <=‘9’) THEN...
How much less confusing to test for c’s value being a member of the set of characters were interested in, using:
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Or perhaps, if we are writing a program to play a card game: 7
TYPE rank =(deuce, three, four, five, six, seven, eight, nine, ten, Jack, Queen, King, Ace ): CardSet = SET OF rank; VAR card : rank; pictures: CardSet; BEGIN pictures :=( Jack . . Ace ): IF card IN pictures THEN { etc. }
Contrast this last example with:
IF (card = Jack) OR (card = Queen) OR (card = King) UB
_ There are also operations defined on sets as a
whole in PASCAL. These are set intersection, union and difference. If B is the set of all BAsic programmers and P represents PASCAL people, then the intersection of the two sets is the set of programmers using both Basic and PASCAL. The union of P and B is the set of people who program in either PASCAL Or BASIC — thatis, the combination of the two sets.
Set difference is, as it suggests, the result of removing or subtracting all members of one set' from the other. Thus, in pascaL notation,
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P — B represents all those who program in PASCAL but not in Basic. Similarly, the notation used for union is P + B, and for intersection P * B. These operator symbols happen to be the same as the well-known arithmetic operators, but the different class of operations should not be confused. Actuaily, the reason they appear so naturally in the context of set operations is that they represent the bit testing that is involved here.
Imagine a set of eight elements. The presence of a particular member could be indicated by setting the appropriate bit in an 8-bit pattern (one byte); absence from the set can be set similarly by a zero. Membership tests, then, just require a mask or bit test, a set union becomes an OR operation and intersection will be a simple AND. These
operations are invariably available at machine
code level, so that the pAscaL compiler is able to provide set data structures and their associated operations very efficiently. The memory overhead is also minimal, and especially when the size of sets can be kept within a computer’s word size ( on 32- bit and over machines, for example), set Operations can be the most efficiently implemented ones in PASCAL. |
ORDER OF PRECEDENCE |
We can now conveniently summarise, all the operators in PASCAL. Those we haven't dealt with explicitly are all familiar from other languages, and PASCAL keeps things extremely simple by only having four levels of operator precedence. Naturally, the ‘unary’ or ‘monadic’ operators take precedence over all the others. These are the symbols + and —, which indicate the sign of a number and the Boolean negation operator NOT. The second precedence level has all the ‘multiplication’ operators (including the division symbols) followed by addition/subtraction and, at the lowest level of precedence, all the relational operators including IN.
Notice that the other two Boolean operators (AND and OR) are treated correctly as multiplying
and adding operators, respectively. This faithfully
echoes the actual Boolean algebra involved, and means that many relational tests are bracketed to override this precedence. Otherwise, for instance: IFN > OANDN < 10 THEN .. will give a compile time error, because the expression 0 AND N (which should be evaluated first) attempts to combine two integer operands with a Boolean operator. Perhaps this is another habit you've acquired from BAsic? If so, now is the time to start breaking it! Naturally, any operators of the same
precedence level are evaluated from left to right, as usual. ‘The symbol used for assignment (:=) has a lower precedence than any of the above operators, as the expression on the right-hand side of an assignment must be fully evaluated before the assignment is made. One word of caution: you can never assume that any part of an expression won't be evaluated, so that: IF (N > 0) AND (K/N < 10 THEN ... could crash a program if N was zero (creating a division by zero error !).
THE HOME COMPUTER ADVANCED COURSE 1115
1116 THE HOME COMPUTER ADVANCED COURSE
Bingo!!
A Bingo card may best be represented by a set. Although the base elements (integers in the range one to 90) are ordered, the only vital consideration Is whether or not a called number is on the card. In PASCAL parlance: ‘number IN Card’ is either true or false.
The program simulates a game of Bingo by first reading the card numbers from the keyboard and then, as each number is ‘called’, testing for the set of called numbers being a superset of the card. The expression Card—Called will become the empty set when every member of Card is also in the set Called.
PROGRAM Bingo ( input, output ); CONST Columns = 40; { to suit VDU } HalfWay = 25; { . } TYPE Bingo = SET OF 1 .. 90; VAR count : | we 10; Allowed, Called, Empty, Card : Bingo; number : integer; House : boolean; BEGIN Empty := [ ]; Allowed := [1 .. 90 ]; WriteLn ( ’*** BINGO ***’ : HalfWay ); WriteLn;
WriteLn ( ‘Enter the 15 card numbers,’ ); WriteLn ( ‘(each followed by RETURN) :’ );
Card := Empty;
FOR count := 1 TO 15 DO
Adding a member to a set that already contains it leaves the set unchanged, aS does ‘removing a non-member. Notice that we cannot add a member to a set directly; but by creating a one-element set by enclosing the number within square brackets, we can obtain the union of two sets.
As it stands, the program will allow duplicated card entries, and will accept an illegal number outside the range one to 90, causing a run-time error. As an exercise, can you think of a simple way of adding loop constructs to prevent both these anomalies and to reject numbers that have already been called?
write ( count : 10, :7? );
ReadLn ( number );
Card := Card + [ number |] END;
WriteLn;
WriteLn ( “EYES DOWN !’ : HalfWay ); WriteLn;
WriteLn ( “Now call each number : “ ); Called := Empty;
REPEAT write ( °? ” : HalfWay ); ReadLn ( number ); Called := Called + [ number ]; House := Card - Called = Empty
UNTIL House;
WriteLn;
WriteLn ( ‘Congratulations !’ : HalfWay );
WriteLn ( ‘Your numbers were :’ ); WriteLn;
FOR number := 1 TO 90 DO IF number IN Card THEN write ( number : Columns DIV 8 )
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Our extended look at the BBC Micro’s operating system has shown how the various ROM routines that make up the OS can be used by the programmer to augment or totally alter the way in which the OS responds to certain situations. Here, we round up the series with several programs that illustrate the uses of OS calls and point to some of their limitations.
aunt
The program we gave as an exercise in the previous instalment (see page 1100), demonstrates how we
an intercept one of the OS vectors in order to change the way in which the OS responds to a certain event. The program alters the contents of OSWRCHV — the vector that holds the address of the OSWRCHV routine. This vector is held at addresses &20E and &20F.
One of the functions of OSWRCH is to take BASIC text and print it to the screen when a program is listed. The main function of the machine code in our program is to look at the ASCII code of each character as it passes through the accumulator
_ during the OSWRCH routine. If the ASCII code is
between 64 and 91 (the character is a capital letter), then 32 is added to the value to give its lower case equivalent. In this way, the program actually forms a ‘wedge’ that will be executed each time the operating system calls OSWRCH. After our code has been executed, control is passed to the real OSWRCH routine using a JMP instruction with the old contents of OSWRCHV. After running th
program, all capital letters in a program listed t
the screen or typed in at the keyboard will b
converted to lower case letters by our wedg
routine. Hitting BREAK restores OSWRCHV to it
normal value.
MEMORY USE PROGRAM This listing is another utility program, which keep
an eye on the use of memory while your programming. The expression:
HIMEM—(?2+256* 73
gives the amount of memory remaining after th
program and variables have taken up their shar
(locations 2 and 3 hold the address of the top of the BASIC variables table). The expression thus indicates how much memory is left for you to work with. However, continuously PRINTing this value can be a little tedious. The routine, therefore, uses the Character enters input buffer event (see page 1099) to evaluate this expression each time a key is
pressed, and sounds a ‘beep’ when the remaining BASIC memory falls below a certain level. The
program is triggered by a keypress event and will continue to operate in the background while you type in your program.
The first task of the program is for the user to determine the threshold at which he wants to be reminded of failing memory resources. This is done by PROCselect-memory, which sets up the threshold in lo-byte/hi-byte form. ‘The program is located at address &0A00, and — as usual for programs that use events — we must first save the contents of all the registers by pushing them onto the stack. After the subroutine that carries out this job is called, the registers are restored and an RTS is executed to return the control of the program to where it was when the event occurred.
The main subroutine calls a further two subroutines to evaluate the amount of memory remaining. The inc routine takes the value stored in locations 2 and 3 and adds the lo-byte and hi-byte of the threshold to it, storing the result in addresses &70 and &71. The sub routine then carries out a 16-
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THE HOME COMPUTER ADVANCED COURSE 1117
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bit calculation, subtracting the contents of &70 and &71 from HIMEM. The value of HIMEM is stored on zero page in locations &06 and &07. Note here how absolute memory locations have been used — mainly because these locations have had these uses in all of the versions of BBC Basic.
After this subtraction has been performed, line
490 checks the sign of the result. If it is a positive .
result, it indicates that there is still more than the previously set threshold of bytes of memory remaining. If the result is negative, there is insufficient memory left, and so it’s time to make a noise about it. The OSWRCH with A=7 call is then made to cause the beep.
The two programs we have discussed so far are simple examples of potentially useful applications.
ie advantage of using the operating system calls tly is that we can generate event-driven code acility unavailable 1 ic. The following
oth use eve
BACKGROUND MUSIC
This program uses the Interval timer has ‘timed out event to play a series of musical notes while the computer performs other tasks. As the event routine runs in the background, you can save a program, edit it, list it or run a different program, while the notes are played throughout. You could expand this program to play a tune while a game program runs, for example. The tune will even be played during disk operations!
The program is assembled to start at address &0C00. The first section is an initialisation routine that performs the following tasks. The event vector EVENTV, at addresses &220 and &221, is changed to point to our routine. OSBYTE 14 with X=o is then called to enable the Interval timer has ‘timed out’ event. A ‘note counter’ at location &70 is initialised to zero, and finally the event timer is
1118 THE HOME COMPUTER ADVANCED COURSE
started by a call to the clock subroutine.
The first task of the event-handling routine is to save the CPU registers on the stack. A subroutine is then called to play a single note and the timer clock is reset. Finally, the registers are restored. One thing to note here is that the register save and restore parts of the program are standard to all our event-handling routines, and we simply change the code between these two blocks of instructions.
Let’s now examine the various parts of the subroutine that play the notes. One note is played, selected from a table of notes, every time the event timer crosses zero. The table of notes, called notetable, is simply a series of bytes holding the pitch information for the five notes that we want tc play. A counter is used to determine which of the five notes is to be played, and the value is held in &70. The pitch value is retrieved and then stored at the appropriate place within soundtable, which is simply the parameter block for the OSWORD routine that we will later use to generate the sound. The counter is then incremented, thus pointing it to the next position within the note table for the next time the routine is entered. As you've only got five notes in the table, as soon as location &/0 holds the value five it is reset to zero.
The subroutine clock uses OSWORD with A=4 to set the event timer running. The area of memory called time holds the value that is to be stored in the - timer registers, thus specifying the time between the notes played. The sound subroutine performs the equivalent of a SOUND command, using. OSWORD with A=7; soundtable is the parameter block for this OSWORD call. The data for notetable and soundtable is set up by the BAsic statements in lines 840 and 850.
Pressing BREAK will stop this program, by resetting the EVENTV contents. However, calling the initialise routine will set things off again.
GRAPHICS MOVEMENT
Our final program shows how we can use events to move a simple graphics shape, in this case a rectangle, across the screen, one position for each
‘event. The frequency of movement therefore
depends upon the value put into the event timer. This value is set up in line 1260. The definition of the shape to be moved, in terms of PLOT numbers, is stored in shapetable and is set up from a DATA statement — line 1220 POKEing the appropriate values in. Lines 1230 to 1250 set up EVENTV to point to our program and enable the appropriate event. Now let’s consider the machine code involved.
This is stored in memory at the address specified by code%. Lines 200 to 230 do the usual register save operation, and lines 250 to 280 do the work by a series of subroutine calls. Finally, we restore the registers and execute an RTS. Lines 370 to 440 save the current status of the graphics cursor and the current GCOL in use so that it can be restored after we've handled the event.
Lines 460 to 520 deal with the movement of the shape. Lines 540 to 630 restore the graphics
colours and the graphics cursor position to the state they were in when we entered the routine.
Lines 650 to 720 use the OSWRCH routine to carry out the equivalent of a BAsic MOVE command to the desired x and y positions. These positions are stored in xpos and xpos+1 for the x co-ordinate and ypos and ypos+1 for the desired y co-ordinate. Lines 740 to 800 draw the shape, again using OSWRCH. The Y register is used as an index register in order to access the table of bytes that represents the shape (shapetable). The bytes are sent as a stream through OSWRCH.
As the shape moves across the screen, it’s clear that there must be routines to update the x and y positions each time the event occurs. This is done by the routines incx and incy in lines 820 to 900. Once the box reaches the top of the screen, the routine overflow resets the x and y co-ordinates to zero. The routine clock uses OSWORD with A=4 to set the event timer off, and the routine gcol does the equivalent operation to a BAsic GCOL3,1
There are several problems associated with this program. Run the code, and as long as the screen doesn’t scroll, the shape will move rather uncertainly across the screen. You can perform other operations while this is happening, and all is
well. However, speed up the movement, by increasing the value in the time area of memory, and although the shape will move when you list part of the program, there could well be unusual characters appearing on the screen. The reason for this is simple — conflict between our routine, which is entered when an event occurs, and the usual OS behaviour when listing. Both require the use of OSWRCH and what happens is that when the OS listing routine is interrupted by our event, OSWRCH is left in a state that the listing routine is not expecting.
If OSWRCH is interrupted, and is called by the interrupting routine, then one exit from the interrupting routine’s OSWRCH call is unavailable. OSWRCH is said to be non-reentrant. This is why Acorn suggest that it is unwise to use OS routines in event- and interrupt-handling routines. You can use them, but you are cautioned to proceed with care. These problems could be overcome by not using any of the OS routines while in an interrupt- or event-handling routine. There are alternatives, such as entering data directly into the screen RAM area to draw graphics, and this is one of the few times where side-stepping ROM routine calls is a good idea.
THE HOME COMPUTER ADVANCED COURSE 1119
Monitoring The Situation
There are two types of monitor: the ‘green screen’ monochrome monitor (most commonly used on business machines because itis the easiest on the eye, and therefore the most suitable for long periods of accounting or word processing). and the colour monitor. The latter category can be further subdivided into two groups. RGB monitors have each of the main colour signals sent down separate cables for maximum definition, whereas composite video monitors send all the signals down a single line
MONITOR
In hardware terms, a monitor is a visual display unit similar to an ordinary cathode ray tube television except that it has no channel selecting facility — it is a dedicated machine to provide a visual display of the video signal from a computer. Monitors produce a much better picture than a standard television screen because the signals from the computer do not have to be ‘modulated’, or adapted to mimic the signal that the television receives from an aerial. Instead, a monitor can process the signal directly into the picture that appears on the screen.
The two most popular types of signals used in monitors are ‘composite video’ and ‘RGB’. A composite video monitor generally has a bayonet- type socket fitted that is a common feature on many video recorders. The colour signals arrive from the computer together and the colours are decoded within the monitor itself. An RGB (red, green, blue) monitor signal is usually sent down a DIN-type socket although there are variations such as the use of Peri plugs. The signal is decoded into the separate colours before it is sent to the monitor, which are then transmitted along three individual lines. An RGB monitor generally provides a better picture than a composite video monitor.
In software terms, a monitor is a program
controlling several independent programs that
may be running at the same time. The monitor will allocate priorities in processor and peripheral time and oversee the progress of each of the programs, passing data between them where necessary. Where a monitor is governing an entire system, the term can be referred to as an ‘operating system’ or ‘supervisor’.
MOTHER BOARD
The mother boardis the main printed circuit board within a computer. It contains all of the major components and systems that are used and often functions without the need for any other boards. The components may consist of the central processing unit, the main memory and the input/ output system. Mother boards generally contain
1120 THE HOME COMPUTER ADVANCED COURSE
slots which allow other boards to be inserted. These additional boards, known as ‘daughter boards’, contain upgrade modules that perform specific additional functions, such as providing additional RAM, an 80-column or colour card, or a printer or disk interface.
In the early days of home computing, when computers were the preserve of electronics enthusiasts, fitting additional boards to a computer became something of a craze as hobbyists competed with each other to customise their machines. It reached the stage where owners of Apple computers could no longer fit the lids on their computers because of all the boards that had been added! Although this still occurs among many enthusiasts, the main customers for daughter boards today are businesses who require additional boards to run specific applications on their personal computers.
MOUSE
Over the past few years the term mouse has come to mean two completely different things. To the home micro user, it refers to a device that is moved around a desk top, which in tum moves a corresponding cursor around the computer’s screen. When the cursor is above acommand or an icon, the user presses a button on the mouse. ‘This
sends a RETURN signal to the computer, which then -
executes the command indicated.
Typically, this device works by having a ball bearing on the bottom of the mouse and a shaft encoder attached to a pair of encoding wheels in contact with the ball bearing. As the bearing rolls across the desk, its movements will be mirrored by the wheels and transmitted through the shaft encoder to an electrical sensor, which sends a digital signal to the computer.
Until 1984, a mouse was considered something of a gimmick among computer users. However, with the launch of the Apple Macintosh, the industry began to realise how useful these devices could be and by 1985 there was a rush to produce
Macintosh mouse-type packages for an increasing
number of machines (see page 1050).
A mouse can also refer to an ‘intelligent’ robotic device that can find its way around a previously unseen maze. Generally, the mouse will have
some kind of sensor system on the front to detect.
collisions, and will either have a system of on- board logic, enabling it to decide in which direction to move next, or else it will be attached to a computer that will provide the processing for it.
The mouse moves through a maze until it encounters a wall, at which point it will attempt to move in a different direction until it finds a way through to the centre of the maze. On its first run, the mouse will ‘remember’ the directions it has travelled, and should be able to find the quickest route through the maze on the second. Robot mice are becoming increasingly popular with robotics enthusiasts and there are now world-wide championships, held annually, to find the world’s fastest mouse (see page 721).
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GUARANTEE GUARANTEE GUARANTEE GUARANTEE GUARANTEE ~~ += =—=—=—se GUARANTEE GUARANTEE GUARANTEE G __ GUARANTEE “Do not affix Postage Stamps f pasted in oN nes ene ea en, ea | ees... _ Gt. Britain, Channel Islands or N. Ireland.
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GUARANTEE GUARANTEE GUARANTEE GUARANTEE GUARANTEE GUARANTEE GUARANTEE GUARANTEE GUARANTEE GUARANTEE . . GUARANTEE GUARANTEE