the ZX-81/TS-1 000 controller:
Contents
1. the ZX 81 TS 1000 controller new use for old computers Four ICs in interface circuit link computer to outside world If you ve been to a hamfest lately or read the back _ pages of any ham magazine you ve probably seen used Sinclair ZX 81 or Timex Sinclair 1000 computers selling for less than 20 During their heyday several years ago these computers which originally sold for 150 led the way for the personal computer rev olution Although the Sinclair was somewhat of a mar vel at the time many users soon became disenchanted with it either because of the small membrane key board or the difficulty of interfacing it with peripherals Perhaps you ve stashed a Sinclair away in your junk box in hope of someday finding something to do with it Or perhaps you ve toyed with the idea of picking one up at a hamfest but decided otherwise Never mind Get one This small cheap soon computer has computing power comparable to much more expensive computer systems The key to harnessing this power is simply finding an application that takes advantage of its strengths For while it s admittedly disappointing for some applications such as word processing it s ideally suited for control functions and can be easily programmed for a host of controller applications TS 1000 computers 19 95 manuals 2 95 and accessories are avail able from Hal Tronix Inc Dep t HR P O Box 1101 Southgate2. Michigan 48195 313 285 1782 In this article a simple circuit using only four ICs will be presented along with a detailed example of how to program your ZX 81 or TS 1000 compulsi for 1 O applications With this simple interface circuit ached to the memory port of either the ZX 81 or TS 1000 you in stantly gain the ability to communicate with the out side world All sorts of applications including satel lite rotor controls digital voltmeters morse code send ing and receiving educational demonstrations and many others easily follow once you have an 1 0 interface developed this circuit as part of a school project a few years ago when used the TS 1000 computer to send and receive RTTY Since then I ve been selling the information contained herein at cost to Sinclair computer enthusiasts at local hamfests and by mail If you ve been wondering how to make your ZX 81 or TS 1000 perform some useful tasks and are interested in a neat one evening construction project then read on what is a controller While many computers are used for computation word processing or data management many small computers composed of just a microprocessor and a handful of special purpose chips are built strictly for controller applications For example microprocessor circuitry is now being installed in automobiles A microprocessor is programmed with a simple looping program which does nothing more than c
3. board fig 2 is shown in fig 3 When mounting the ICs be sure to use a low wattage soldering iron since the pads are delicate strongly recommend the use of sockets for each of the four ICs All of the components are easy to acquire at ham fests or electronic shops except perhaps for the 46 pin connector used to attach the interface board to the computer memory port The connector type is the same as that used on ZX 81 and TS 1000 peripher als such as the 16K RAM pack and is a 46 pin double sided edge connector with 0 1 inch spacing between contacts found that you have to buy a sturdy con December 1986 33 ceococooonooooooeosco eeocoeooocooooooooeocs eceooecooogooooeooooso ceceooocoooooooooeooooo0so eccoooocoooooocoooco9g0o00o COCOCCAOCrvccs c2000000 0000 COOCCOOrc270x200 0200000 OGQ0OGCODccxv00000000000 eCeeceoeceeOrvro0co00000 000000 eCQC0CCOCCrreccrc00007000000 C 00O0C0G02270Z0000000000 0000 0000 0000 0000 e000 e000 oo00 0900 oo000 0000 0 0 00 0000 409 0 00000000000 LB 320999 G00000000 Table 3 Jumper wires needed for single sided circuit board These connections should be made after all other components are soldered in place Jumper between U1 pin 11 and U4 pin 36 Jumper between U2 pin5 and EC1 pin 19B Jumper between U2 pin 6 and U3 pint Jumper between U3 pin 2 and EC1 pin 7B Jumper between U3 pin 3 and EC1 pin 8B Jumper between U3 pin 8
4. your machine code the REM state Table 4 Machine code for programming example Assembly language instruction Machine code LD A 144 OUT 127 A INA 115 JRZ 4 LD A 255 OUT 119 A RETURN TO BASIC ment appears as gibberish on the screen For the TS 1000 computer the first usable memory slot once a REM statement is entered is 16514 Use the POKE command to place the machine code in sequential memory locations starting with 16514 Upon complet ing the entry of your machine code place the opcode 201 in the very next memory location following your last program opcode At this point it s a good idea to save your program on tape even though it s only a single REM statement That way if anything happens for example if junior unplugs your computer you don t have to re POKE your entire program For the machine code in table 4 the following would be en tered into the computer POKE 16514 62 press enter POKE 16515 144 press enter POKE 16516 211 press enter POKE 16524 211 press enter POKE 16525 119 press enter POKE 16526 201 press enter To verify that the opcodes are in memory you may use the PEEK command to see what the computer has stored _ In order to execute your machine code you must have a BASIC statement that contains the USR func tion For the window alarm program your next pro gram line following the REM statement could be 2 LET WINDALARM USR 16514 By running th
5. ad the status of each win dow into the computer If we use a simple transistor switch to activate the bell one of the pins from Port B can be connected to the gate of the transistor switch When a window is discovered to be open the computer then sends out a high logic level 5 volts to the alarm pin as well as the unused pins on Port B thus sounding the bell The programming steps for the window alarm ex ample would be as follows 1 Initialize data flow on Ports A B and C 2 Look at input data from windows 3 If any of the input data bits is 1 sound alarm 4 If the input data is all 0 then go to step 2 Notice that once the data flow is initialized on U4 no further action is required unless the power is un plugged or U4 is reprogrammed The assembly lan guage program for this example follows comments are included in parenthesis Initialization LD A 144 144 10010000 This programs Port A for input Ports B C for output We load 144 into ac cumulator OUT 127 A Send contents of accumulator 144 to the U4 control register which is located at ADDR 127 Monitor window data loop N A 115 Read in the eight bit data at ADDR 115 Port A and place data in the ac cumulator JRZ oop Compare the eight bits of data in accumu lator to the all zeros data word 00000000 if all eight bits of data are zeros then jump back to oop and continue to monitor _ If pro
6. and U4 pin 6 Jumper between U3 pin 16 and U1 pin 16 Jumper between U4 pin 8 and EC1 pin 10B Jumper between U4 pin 9 and EC1 pin 9B Jumper between U4 pin 27 and EC1 pin 1A fig 3 Component layout for interface circuit view from component side EC1 mounted on FOIL SIDE nector and be prepared to use a Dremel tool or a small saw to cut a larger connector down to correct size But be careful bought a 60 pin double sided con nector for less than 1 00 from a military surplus dealer at a hamfest Eagerly took the new connector home cut it to length and soldered it onto the board After a couple of trial fits on the memory port of the com puter the connector crumbled into tiny bits It was a real pain to have to chop off the faulty connector and resolder a new one onto the board You may no tice from the accompanying photographs that the con nector must be soldered on the foil side of the board and protrudes from that side of the board as well The entire cost of components is well under 20 The construction time is fast one evening should be sufficient was able to find attractive plastic boxes made by UNIBOX at a loca Radio Shack for less than 4 00 each The circuit board fits neatly inside and only two rectangular holes have to be cut into the box a 0 5 x 2 5 inch hole to allow the 46 pin edge connector to protrude from the circuit board and a 0 5 x 1 0 inch hole on the othe
7. and the computer In table 2 I ve shown the addresses used to control the _ various registers of U4 While some of the basics on how to use U4 will be spelled out later more details can be found in any Intel databook or in Goldsbrough s Microcomputer Interfacing with the 8255 PPI Chip When laying out a circuit board decided that it would be nice to have the ability to add components or connectors in the future I call the upper portion of the board where there are several inches of 0 1 inch spaced holes the playground area By adding com ponents and appropriate jumper wires it s possible to expand the interface circuit The single sided board negative used shown in fig 2 requires ten insulat ed jumper wires which should be installed on the foil non component side of the circuit board after all of the components are mounted see table 3 Pads are available on the circuit board to permit easy soldering of each jumper used 16 additional jumpers to route all eight of the port A pins four of the port B pins and four of the port C pins from U4 to molex pins at tached on the top of the playground area These molex pins mate with headers that allow for easy de tachment of the data lines from O hardware or from a case mounted connector You may wish to use just one pin or all 24 pins available on U4 for I O data ex change Use as many data lines as you need The component layout for the circuit
8. d sent as control signals to external hardware I O devices Similarly in conjunc tion with the interface circuit the computer can read in very fast asynchronous signals from external hard ware and use the received signals to make decisions in software Figure 1 is the schematic diagram of the I O inter face A complete parts list appears in table 1 Note that no power supply is needed for the interface all four ICs are conveniently powered by the computer s internal 5 volt supply the voltage is made available at the computer port The heart of the interface circuit is U4 the 8255 programmable peripheral interface PPI chip U1 U2 and U3 serve to decode the address signals generat ed by the computer After much trial and error found that it s possible to access four 1 O address locations not used by any of the internal computer circuitry These address locations 115 119 123 and 127 Table 2 Operation of 8255 PPI chip U4 I O instruction I O Address Operation IN 115 Read from Port A IN 119 Read from Port B IN 123 Read from Port C OUT 115 Write to Port A OUT 119 Write to Port B OUT 123 Write to Port C OUT 127 Write to Control Register decimal may be used to activate any external de vice connected to the computer port For my inter face circuit these four address locations are used to access U4 which in turn directs the flow of data be tween any external O device
9. e Department Intel Corporation 3065 Bowers Avenue Santa Clara California 95051 2 P F Goldsbrough Microcomputer Interfacing with The 8255 PPI Chip Howard W Sams Publisher 1979 3 UNIBOX Amerex Corporation Riverside California 92502 4 Michael Hordeski Microprocessor Cookbook Tab Books 1979 ham radio AVAILABLE NOW THE 1987 ARRL HANDBOOK The latest edition of the Ham s bible has been updat ed with plenty of exciting new projects new theory and information chapters and the latest in state of the art technology Check out these new features Passive LC filter design including standard value capacitor tables overview of 23cm FM fast scan tv weather satellites basics a complete revision of the radio frequencies and transmission section chapter 22 and satellite communications section chapter 23 Some of the exciting new projects are a new hf legal limit all band amplifier using the 8877 tube a dedicated CRT for Wefax image display and a new marker generator project for general use to name just a select few Over 200 pages have been revised and updated Great reference book that should be in ev ery Ham s shack Order your s today Over 1100 ages 1986 ae ORDER AR HB87 YOURS JAR BB87 NOW available in December Softbound 17 95 Hardbound 26 95 Please enclose 3 50 shipping amp handling 1 ntel is a trademark of Intel Corporation Information on Int
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11. gram gets to this point then sound the alarm LD A 255 Load accumulator with all ones word 11111111 OUT 119 A Send the accumulator contents out to Port B this sounds the alarm oe Beans Fe a pa Pyle ANIAR tee Bete eter a Aaa rt eas A gt The preceding assembly language program when written in machine code requires only 13 bytes of memory It s entered into the computer via the POKE _command The conversion from assembly language mnemonics to machine opcodes is given in the ZX 81 and TS 1000 user s manual appendix For the previ ous program the machine code that would be POKEd is given in table 4 Although not illustrated in this aan it s snipe to monitor your O activity by going back and forth between BASIC and machine code In this case it would have been easy to see on the computer moni tor which particular window or windows were opened by simply passing the Port A data to the b c register pair in the machine code program and then by returning to BASIC by way of the USR command and printing the value of the USR function on the screen machine code within BASIC programs To store a machine code program in the computer you must first set aside some memory by using a REM statement usually the first line in your BASIC pro gram The REM statement sets aside successive memory locations which are never written over there by allowing you to store machine code programs safe l
12. ions the computer is programmed to handle a var iety of input signals from external hardware and issue 32 December 1986 Table 1 Parts list for Interface Circuit fig 1 Schematic Designator Description C1 4 7 pF electrolytic capacitor C2 0 01 aF capacitor C3 l 0 01 xF capacitor EC1 2 row x 23 pin edge connector 0 1 inch spacing pin length at least 0 75 inch DB 25 D onnector 74LS32 Quad two input OR chip 74LS00 Quad two input NAND chip 74LS30 Eight input NAND chip 8255 Programmable Interface Chip Miscellaneous Single sided circuit board Jumper wires at least 10 Project box UNIBOX UB270 130 control signals to external hardware Because the con troller s program is simple and repetitive it doesn t re quire much memory The 2K of memory in the ZX 81 and TS 1000 is more than enough to program even a very complex controller We can also take advan tage of the computer s high level BASIC capability to simplify programming the computer for controller applications An understanding of machine language is important though since the I O interface must al low exchange of data on a level lower than BASIC this is done through the PEEK and POKE commands description of interface circuit With the interface circuit connected to the port of the ZX 81 or TS 1000 very fast data signals which ap pear on the data bus of the computer can be latched by the interface circuit an
13. is article to teach assembly language and machine code programming let me assure you that mastering them is not difficult If you find the example in this article insufficient you may wish to read Chapters 1 2 and 5 in Hordeski s easy to read Microprocessor Cookbook The following example details the simplicity of con troller software Consider an alarm system that moni tors the status of eight windows around the house Three wires ground 5 volts and data status line could be routed to each of eight windows A small switch could be mounted by each window so that if fig 4 The circuit board fits into the project box Be sure to use an edge connector with at least of pin length to allow clear ance when the circuit is plugged into the computer port It is convenient to have a connector on the back of the box for easy access to the I O lines 38 December 1986 the window is shut a low logic level 0 volts exists on the status line If any of the windows are open we want the computer to recognize this and sound a bell For this case we may use all eight pins of Port A for input to read the status of each of the eight win dows and may use Port B for output although we need to use only one of the eight pins to output a con trol signal for the alarm Since we re not using Port C we don t care what it s programmed for By con _ necting the status line of each window to individual pins of Port A we can re
14. is simple two line BASIC program your Sinclair computer executes the machine code and is able to communicate with external devices through the use of the interface circuit If the machine code was written so that the Port A data was placed in the b c register pair then the value of the variable WIND ALARM which can be viewed on the monitor with a simple print statement such as December 1986 39 Ca CON TPE ANE AL AO SOOT DOE ae a ee Be RECEIVE THIS LCD ALENDAR LOCK FREE ITH YOUR UBSCRIPTION A WHAT S REALLY HAPPENING IN HOME SATELLITE TV THE HOME SATELLITE TELEVISION MAGAZINE A monthly of 100 plus pages has everything you need to know about where to find equipment how to install it system performance legal viewpoints and in dustry insights With your subscription to STV you will receive a FREE LCD Calendar Clock e Only 19 95 per year 12 monthly issues e 1 00 for sample copy IF YOU HAVE A SATELLITE SYSTEM THEN YOU REALLY NEED The best in satellite programming Featuring All Scheduled Channels Weekly Updated Listings Magazine Format Complete Movie Listing All Sports Specials Prime Time Highlights Specials Listing and Programming Updates e Only 45 00 per year 52 weekly issues 2 Years 79 00 104 weekly issues e 1 00 for sample copy Visa and MasterCard accepted subscrip tion orders only All prices in US funds Write f
15. ontinuously monitor various data lines and then branch to a par By Ted S Rappaport NONB Box 283 Electri cal Engin ering Purdue University West Lafayette Indiana 47907 December 1986 31 FROM SINCLAIR COMPUTER PORT TO 1 0 DEVICES PI fig 1 Schematic diagram for interface circuit ticular part of the program when specific lines change state These input output 1 0 lines are connected to hardware such as the fuel level sensor the climate control console and thermal sensors under the hood and inside the passenger compartment When the driver wants to raise the car s interior temperature to 75 degrees he or she simply presses a button enter ing the desired temperature The program in the micro processor is continuously looping searching for any changes on the input data lines Finding that the driv er has activated the climate control console line the program then branches to the subroutine designed to effect the desired climate change In this case the in formation 75 degrees is read into the microproces sor as digital data and a control signal is then sent out to the appropriate hardware in this case the heater on off switch While this is an overly simplified ver sion of what is actually done in today s automobiles it illustrates one typical application of a controller Of key importance is the fact that in such applica t
16. or foreign rates Send this ad along with your order to STV OnSat P O Box 2384 Dept HR Shelby NC 28151 2384 TOLL FREE 1 800 438 2020 40 UN December 1986 7 202 SUBSCRIPTION CALLS ONLY _ 3 PRINT WINDALARM could be displayed to indicate in decimal the win dow status When using the Sinclair computer as a controller more than one machine language program can be used It s often convenient to write several subroutines in machine code and store them all in succession in the first REM statement Remember they re separate to the computer when they end in the opcode 201 In this manner your BASIC program can consist of various calls to the subroutines by using USR func tions with the appropriate memory addresses in the REM storage conclusion In this article I ve discussed the hardware and soft ware needed to provide a communication path be tween your Sinclair ZX 81 or Timex Sinclair 1000 computer and any O device you might wish to con trol or monitor With the price of these computers so low even those with the tightest budgets can afford to experiment with computer control By now you may already have an idea for a controller application in your shack If you take an evening out to build this circuit and spend a few hours reviewing machine lan guage programming you ll be amazed at what your small but mighty computer can do references be obtained from Literatur
17. r side of the box to allow O wires to be fed to a D connector mounted on the exterior see fig 4 interface software You can add all the hardware in the world to a com puter but it won t serve any useful purpose unless you know how to program the computer effectively In this section a programming example for an application of the interface circuit is given and a review of how to 34 December 1986 E E T et at LAEE at dae eo be use the ZX 81 and TS 1000 PEEK and POKE com mands is presented In order to perform data exchanges between I O devices and the computer it s first necessary to set up the I O format on U4 U4 has 24 pins which are usable for data exchange These pins are partitioned into three groups of eight pins Each group of eight pins is called a port Any program written for 1 0 control should begin with an initialization stage This initialization sets the data flow of the ports on U4 For example you may want to program the eight data lines of port A for out put data sent to the 1 0 device from the computer and have the eight data lines of port B programmed for input data sent from the I O device to the com puter While ports A and B require that all eight pins be either input or output Port C allows for four pins to be input and four to be output Of course Port C may also be programmed for all eight pins to be either input or output While it s beyond the scope of th
18. y Machine code programming may be saved on tape by using the SAVE command A machine code program is run in sequence by us ing the USR command where the argument of the USR command is the address location of the first ma chine language opcode The computer returns to the BASIC program once the return opcode 201 is en countered and assigns the decimal value of the b c register contents to the variable name to which the USR function is equated In this manner it s possible to pass data from machine code programs and con sequently data from external I O devices to BASIC Or you may use the PEEK command in a BASIC pro gram to retrieve data from dedicated memory locations in your machine code storage area REM statement Either way it s a simple chore to transfer data from real world devices to your computer By using the POKE command in a BASIC program you may place data from BASIC into data locations of machine code programs Note that this allows you to make keyboard entries and have these entries correspond to control signals for 1 O devices When you re ready to enter a machine code pro gram into the computer clear the computer s memo ry and begin as if you were writing a new BASIC program Enter line 1 as a REM statement filling in as many letters in the REM statement as the number of bytes required in your machine program It doesn t matter what you put in your REM statement because after you POKE in
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