ZX Computings - OpenLibra

More documents

Recommendations

Info

Adding a numeric keypad 32 if your ZX81 is employed for business or mathematical use, you'll find this project — a numeric keypad — a worthwhile one to build. Taken from the book "20 Simple Electronic Projects for the ZX81", by Stephen Adams, this article discusses the role of an INPUT/OUTPUT port, and then explains how to use this information to help you build a numeric keypad for your ZX81. ZX COMPUTING AUG/SEPT 1982 4
Construction c 1 1 1 1 32 Bit 7 Bit 6 Bit 5 Bit 4 Bit 3 Bit 2 Bit I Bit 0 In order to make the ZX81 more useful, and allowing it to control things, we must first be able to send signals to and from the ZX81. A device to do this is called an INTERFACE. A common interface is an INPUT/OUTPUT port, this consists of one or several chips which will store any data sent to it and keep it available for an external device. It will also allow you to "see" through it to an external device. The maximum amount of data that it can store is eight Binary (TWO STATE) BITS, which consist of eight wires which have either + 5 volts (binary 11 or 0 volts on them. The IN- PUT and OUTPUT ports are usually separate, so the data emitted by the output port is not affected by "reading" the input port. To tell if it is a READing operation or a WRITEing (OUTPUT) operation the ZX81 puts out two signals NOT WRITE (WR) and NOT READ (RD). The fact that either of these signals is at 0 volts (Binary 0), enables the operation to be done. The device also requires a place whe. i you know that you can collect and send your data. It is called an ADDRESS. The address applies only to this port and no other piece of equipment connected to the computer. The ADDRESS wires A0-A15 contain *his number when the ZX81 wants to talk to your port. There are several companies which produce IN- PUT/OUTPUT ports for the ZX81, but their ports fall into one of two categories. One of these requires a special machine code routine to be written in order to get the data to and from the port. This is because they are treated differently to a normal memory location. They are in a separate memory map to the RAM (Random Access Memory), controlled by a signal called NOT IN- PUT/OUTPUT REQUEST (I0REQ). When this line is at 0 volts ALL memory is switched off the memory map and f A11 / ON ZX81 \ A12 I \ A8 replaced by locations numbered 0-255. Thus on IN- PUT/OUTPUT signals only AD- DRESS lines A0-A7 need to be used. BUT because this is not available through BASIC, a special machine code routine needs to be written. The other type of port is a MEMORY MAPPED port, which is treated like a piece of RAM. It may be PEEKd (transferred from the port into the program) or POKEd (transferred to the port from the program). The ZX81 is not supplied with a users port, so one must be externally attached. The PEEK and POKE are BASIC commands and can be included into a program in the following form: PEEK 16396 POKE 16396,255 PEEK returns the number between 0 and 255 (the maximum number of combinations available from 8 bits). POKE puts a number between 0 and 255, which is after the comma, into the location in memory which is before the 1 Number 28 -16 12 - 8 Bit 5=1 Bit 3 = 1 J" MM ft vf-v. J'X. KBD4 KBD3 KBD2 KBD1 ;e 6 p 8 p 9 S H comma. No matter what method you use, you can only put in a number between 0 and 255. This is because we only have 8 bits (1 's or O's) at each location. These are numbered Bit 0 (BO) to Bit 7 (B7), and shown in Fig. 1). Each bit represents a number in the multiplication table. The bit number gives the number of times 2 must be multiplied by itself, if it contains a BINARY 1(1), ie. if Bit 3 is Binary 1 then it represents 2 x 2 x 2 or 8. If it is Binary 0(0), then it represents exactly that 0. One thing to watch out for is Bit 0, when it is Binary 1, represents an odd number eg. 1. An example is that, if Bit 7 and Bit 0 are Binary 1 and the rest are Binary 0, it equals 1 28 + 1 (129). Try this for yourself with different numbers from bits to numbers and back again. If you have trouble with converting numbers into bits then try this. Subtract the highest number below yours scoring a Binary 1 in this bit. Then do it again until you reach 0. 4 Bit 2 = 1 -4 Number 28 = 00101 100 ON ZX81 All the rest of the eight bits must therefore be O's. The ZX81 keyboard is a matrix of switches which each connect ONE address line and ONE data line input. As there are five data inputs (KBDO- KBD4) and eight address lines to the keyboard, the maximum number of combinations is forty (8 x 5 = 40) keys. The numbers keys are usually the most used, and are not very convenient keys to use when great accuracy is required. If you use number keys a lot in games or business programs, you might like to build a separate numeric pad. This will enable you to speed up the entry of numbers because you can 'feel' the keys positively hitting the end stop, and thus release it quickly. As the Sinclair keyboard is made out of three thin pieces of plastic film, there is very little distance between the top and the end stop of the key movement (0.1 inch). It is therefore not easy to tell whether you have pushed the key down far enough to make the switch close. The movement of most keyboard "PUSH TO MAKE" switches is at least 0.5 inch, which gives the keys much more positive feel when pressed. The best type of key switches to use are those with a removable clear plastic top. You can then place a piece of paper under the covers, on ZX COMPUTING AUG/SEPT 1982 49
Page 1 and 2: QsMTPQMK]® Britain's Biggest FOR T
Page 3 and 4: Fully cased keyboard £37.95 Uncase
Page 5 and 6: ZX Computing is published bi-monthl
Page 7 and 8: So as a business machine it really
Page 9 and 10: r « te i? ell ce • No-one asked
Page 11 and 12: "...the quality of the colour displ
Page 13 and 14: as ! Cassette £6: Fun to Learn ser
Page 15 and 16: to n The following week, at a ZX Mi
Page 17 and 18: ZX COMPUTING AUGUST/SEPT 1982 17
Page 19 and 20: an )ms 2 at ing out TO, if wn md th
Page 21 and 22: 2 9000 901© I" C'LS PRINT 9020 PRI
Page 23 and 24: two ; rom and The J as sive >!ied ;
Page 25 and 26: word Games The spectral Hangman rid
Page 27 and 28: " 260 PRINT CHR5 FL (133 ;CHR$ CHR$
Page 29 and 30: 32 The second program, MPRF, is a g
Page 31 and 32: 795 5'00 •BIG S20 33© 1O0) 540 )
Page 33 and 34: The printout shows you what the scr
Page 35 and 36: OHMRND" 90 PRINT RT 1 3 , 2 ; " N ,
Page 37 and 38: 18 PRINT "NUMBER OP WORDS TO E £ S
Page 39 and 40: 'LIT N y RRT >' • m / L- >y R . u
Page 41 and 42: shown in the manual, then typing in
Page 43: Graphics The PLOT thickens The IF..
Page 47 and 48: ions cuit only :on- The eys y to at
Page 49 and 50: !28240 • Lines 390 to 480 single
Page 51 and 52: 1 There's no special reason for our
Page 53 and 54: [ Sample printouts from J. K Graye
Page 55 and 56: I V i If you've ever struggled with
Page 57 and 58: 5 PRINT "SEEK" 10 DIM P(2) 20 DIM Z
Page 59 and 60: Machine Code Figure 1. 01 1A00 LD B
Page 61 and 62: Book reviews Caring for your comput
Page 63 and 64: is a characteristic of earlier Time
Page 65 and 66: Sorting it out This utility program
Page 67 and 68: Colourthello is intended to highlig
Page 69 and 70: 0 Level Physics Paul Holmes from Su
Page 71 and 72: DO you use A CASserre DCCH WITH YOU
Page 73 and 74: 60 PRINT BT 2,3; M i i W M T T T f
Page 75 and 76: ZX81 Spectrum 16K 1 MANAGEMENT GAME
Page 77 and 78: Some BASlCs do not allow a computed
Page 79 and 80: t an ling idile it /erto the EN >nt
Page 81 and 82: AS and B$. A$ holds information con
Page 83 and 84: 220 LET B1=P 225 LET Lfl=i 230 LET
Page 85 and 86: Vegas Breaker Chuck Hopper's progra
Page 87 and 88: y y Personal Software is a new quar
Page 89 and 90: ZX80 Carries 150 LET D = 0 350 IF B
Page 91 and 92: Graphics User-definable graphics Th
Page 93 and 94: frame counter as a timer use this r
Page 95 and 96:
Specialist Book$ Choosing program*
Page 97 and 98:
The Spectrum Listing 5 REM * MRTCHS
Page 99 and 100:
Make sure you get every issue of ZX
Page 101 and 102:
Business Keeping tabs on your chequ
Page 103 and 104:
JRS SOFTWARE 19 WAYSIDE AVENUE. WOR
Page 105 and 106:
11SO GOTO 1030 1150 LET X$ = X $ (
Page 107 and 108:
The variables used are as follows;
Page 109 and 110:
MELBOURNE HOUSE • ZX81 • SPECTR
Page 111 and 112:
L£T B=B+1; BEEP .2,B*2S -4.0 LET G
Page 113 and 114:
5 REM Pro g r am three 10 LET a$=CH
Page 115 and 116:
2° Cassette E3: Fun to Learn serie
Page 117 and 118:
ZX80 Dimensions Width 174mm (6.85 i
Page 119 and 120:
Mathematical Operations And Functio
Page 121 and 122:
FULLER FD SYSTEM £39*95 Profession
show all

ZX Computings - OpenLibra

Create successful ePaper yourself

Delete template?

Save as template?