TRS-80

[chipfryer27]

Hi

I another post I started to document my TRS-80.

The Tandy Radio Shack 80 was based on the Zilog Z-80 processor and introduced to the world in 1977 when I was in my early teens. For most the only information on this new exciting field of "small business / home computing", which being honest was financially still out of the reach of most, was contained in magazines either dedicated to this new technology or in the electronic magazines of the day. I still drool at pictures of the Commodore PET (personal electronic transactor) which I suspect was inspiration for Dr. Who's dog, K9.

At the time, broadly speaking you had the choice of the PET or an Apple, with the latter costing way, way more for no obvious to me reason. Tandy (Radio Shack) employed an engineer to design a machine to compete in this new market. This cost the company approx $150,000 to develop and the TRS-80 came to life with a price tag of around $599 (with monitor and cassette storage), which was less than the PET (not yet shipping) and around half the price of the Apple. Top management, although obviously signing off on the project in the first place, felt that the market would be for 3500 units (coincidentally one for each store) and gave the order to proceed with the notion that if it failed to sell at least they could be used for stock taking.

Tandy announced it's creation at a press conference and the TRS-80 made an appearance at a fair a couple of days later, shortly after which Tandy had orders for over 15,000 units with a waiting list of around a quarter of a million, paying deposits. Astounding.... Within a few years Tandy could claim the TRS-80 to be the best selling computer in the market and for themselves to be the biggest manufacturer of computers (outselling Apple five to one).

The story of theTRS-80 really is an interesting read, especially the problems they had to overcome as few took them seriously. The colour scheme of the units, black and grey, were solely to match the existing colour scheme of the only company willing to supply them with monitors. Incidentally there is no lower case as that would have cost an additional dollar or so in manufacturing costs.... I would encourage anyone with any interest to search for this amazing little machine that did change the face of computing.

Now any of the "Holy Trinity" of machines as the TRS-80, PET and Apple were called at that time was way, way out of my reach. I did obtain a Science of Cambridge Mk14 as a Christmas present that year which was based on the SC/MP processor and I loved it. I had to construct it myself but rather than just assemble it asap I figured out what was doing what first, so I knew I was soldering in sockets for the RAM etc. I guess I was the school-kid equivalent of Steve Jobs as I put my Mk14 into a wooden case, but only found out Job's did that too years later...... Maybe if I'd been at Uni in 77 things may have turned out differently for me.......

In November 1980 I entered the new and exciting shop of Tandy in Glasgow and bought a TRS-80 16K Level II machine complete with green screen monitor (16 x lines of 64 x characters) and cassette deck. The 16K referred to the amount of Memory and Level II was their latest BASIC. This machine was a big deal, make no mistake about that. It was being used globally by businesses and hobbyists (not sure if geek had yet been applied to anyone that knew what a computer was). I think it cost me around £500 or so, which could have bought you a decent second hand car at the time. I bought a couple of games at the same time, one a text based adventure in which you explore a Pyramid, and another that saw you commanding a starship. The display for that game was cool despite the limitations.

Programs were loaded / saved to/from a cassette deck, and getting the volume correct was sometimes a pain. Although in saying that once you found the correct volume level on the TRS-80 it generally worked fine thereafter.

For the next few months I was never away from it, learning not just the BASIC language to make it do things but the schematics too. I harboured ideas to connect it to the real world and did manage to interface it BASICALLY (pun intended). Every trip to Tandy included looking at whatever new titles they were stocking in their Manuals section and I acquired many including "The Technical Reference Manual".

Tandy in hindsight did make a mistake by not selling any 3rd party software in their stores, only official "Tandy" software which may not have been as good as they hoped (Mr. Gates I'm looking at you......). However before being overly critical you do need to remember that the whole industry was in its infancy and if you bought a computer you really were expected to write your own program(s).

As an aside, the early 80's also saw an explosion of Video Rental stores and one local to me bought a computer running some form of DOS with two 5.25" floppies (before IBM and their "PC"). They also got a database program to track members, titles, hires etc. This was clunky to say the least requiring swapping of floppies per transaction.... Things slowed further as membership grew. I was asked if I could help by "fixing" the code or writing a better program. I was offered "free" membership in return...... You can probably guess the rest.

Over the next few years computers rapidly advanced. Even IBM got in the game...... My TRS-80 started to get lonely as it was being used less and less. I'd bought other more capable machines and it was slowly getting pushed off my desk. I'm guessing, but thinking on it I probably last used it for any purpose mid 80's and the last time I switched it on the display didn't show anything so it was consigned to the loft, where it has lived for almost forty years. I have to say though that the BASIC principles (again pun intended) learned on that machine stood me in good stead for many years.

A few weeks ago I decided to fetch it out. I found the computer in it's original box with PSU and cassette leads, the monitor (video plug damaged) but couldn't find the cassette deck nor any software. They may still be in the loft but I'm not too hopeful. Many memories returned...... Taking it to the evil lab I gave it all a clean. The actual computer is a one piece affair with the electronics mounted underneath a mechanical keyboard. I had no issue at all with the keyboard but being open keys I did hear of issue with dust / liquids.

The TRS-80 16K Level II computer

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After cleaning it up I checked the PSU which was still within limits. Really glad of that as the PSU is in a folded metal case held closed by rivets. I then opened up the computer to have a look inside. I have to say I'm still impressed with it's solid construction. The decoupling capacitors seem to have a white coating due to ageing but other than that they checked fine with my LCR tester. The 10,000uF capacitor hadn't faired as well with bulging clearly visible.

TRS-80 PCB

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Failed capacitor

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10,000uF capacitors are quite expensive, surprisingly so, therefore I swapped it out for 2 x 4,700uF in parallel which would be near enough to see if it actually still worked. Connecting the PSU (all plugs are 5-pin DIN) to the correct socket I checked voltages. I am amazed that they were all still within limits albeit some only just. A tweak of a pot brought them to what they should be. The excitement of seeing my machine potentially come back to life is not to be underestimated.

Case refitted which took a bit longer than expected as the case screws are of differing lengths..... yeah, yeah, you've all done the same....

With nothing connected to it I powered up the monitor. This still has the original 2-pin mains plug as seen on any electric shaver, having never gotten around to replacing it with a 3-pin fused one. The display slowly warmed up and gave a relatively bright green screen. This wasn't good as having no input it shouldn't be displaying anything (think running a "whiteout routine", and if you remember them you are showing your age). The 5-pin DIN was broken, looking like it had been stepped on so the monitor was side-lined until new plugs were obtained.

As I'd bought my machine complete with monitor I had no composite to UHF converter, but I do have the Technical Reference Manual so I could figure out what pins did what on the video socket.

The socket had Ground and Composite Out pins but unexpectedly it had a +5v Out too.... More on this later.

Using jumpers from the pins to a cannibalised Phono lead I had a composite video, I just needed something to plug into. I had a couple VHS recorders and DVD players in the loft so with the help of some SCART connectors I could in theory go from computer to VHS via composite to SCART adapter then out on UHF to a TV. No luck, but thankfully I couldn't get anything to display via the SCART so it didn't mean the TRS-80 was at fault. I ordered up a composite to HDMI converter from a well know online source. Quite by chance a day or so later I came across an old flatscreen Samsung TV that had composite inputs. With this back in the evil lab I connected up the TRS-80 and was very happy indeed to see the familiar question "MEM SIZE?" (remember no lower case) and after a tap on the "ENTER" key I was given the "READY" prompt. To say I was very happy at this is a gross understatement. My machine, forty three years old was still working (with only one duff capacitor failing due to ageing). I find that remarkable and a testament to engineering of the time. When the HDMI converter arrived it did work but not too well. It's fine with pretty much anything but the computer. With it connected the display flickers too much to be of use. I'm guessing the read/write cycle is the cause but not to worry.

With new Din plugs I went to work on the monitor. As mentioned nobody took Tandy seriously when they sourced parts but RCA agreed to supply them with a TV that had the tuner and sound stripped out. However as the chassis was floating it couldn't be connected to the TRS-80 ground. The solution was opto-coupling which is why the video socket on the computer has a +5v pin.

I'm no TV repair man but I know enough about tubes to pay attention to the Left Hand Rule. That is when working with them keep your left hand in your back pocket or risk death.....

Removing the monitor cover I was greeted by a Samsung tube and not an awful lot more.

Inside the monitor

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Fiddling with any of the controls saw the display go from whiteout to blank etc so I though that connections may be dirty. A liberal scoosh of contact cleaner in every pot I could see and also on the tube adjustment rings happily restored the monitor to what appeared to be normal.

Do you want to adjust these tabs whilst live?

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I did notice that my monitor has no opto-coupling. As it was for export it has a stepdown transformer to drop our 240v down, negating the need.

With it all back together I connected the computer and with some trepidation I first switched on the Monitor. A dark background with just a hint of green appeared (yes it was actually on...) I then switched on the TRS-80 PSU and pressed the On button.....


Back to life

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I did have to make a few adjustments to the monitor to centre it correctly after cleaning the pots / rings but these were trivial and I'm very pleased that it too, after forty years, still works just needing a clean.

TRS-80 16K Level II

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Of course no visit to 80s computing would be complete without the obligatory BASIC loop


As seen in every store window (change target to suit)

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The TRS-80 has an expansion port at the rear, which is basically just part of the PCB and gives full access to the Address Bus, Data Bus and a host of other lines.


Expansion Port

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You might be wondering what an article on an ancient computer is doing on a forum for microcontroller programming? Well,it is to do with the above expansion port... I'm not going to ask Matrix to port a version of FC to create my Level II programs, but if they want to I'll happily test...

I love my TRS-80 and I want it to be doing something. I'm not going to do payrolls or try and host a database as it is impractical, but it must surely still have a use?

The TRS-80 is memory mapped so there is potentially thousands of available ports that can be used, each 8-bit wide. In addition, Level II brought Port commands whereby you address up to 256 Ports negating the need to decode all address lines.

I'm looking for ideas as to what I can use my TRS-80 for. One idea is to connect it to a PIC (or whatever) running Flowcode using the expansion port. Say the PIC is constantly performing ADC on a specific pin. If I send a command from TRS-80 to PIC it will return the ADC value. Same for DAC.

I'm sure you get the idea. The PIC is the interface being commanded by the TRS-80 to do something. What is that something or some things?

Regards

[mnfisher]

Thanks, that's fascinating. I only wish I worked as well as I did 43 years ago.

Martin

[BenR]

Some great info there takes me back to my school holidays with time well spend learning basic on the borrowed school bbc micro.

[chipfryer27]

Hi Benj

When I think back now on what was then cutting edge, and the innovative ways employed to get the end result, I think I can say that they were very exciting times. You couldn't just throw machine power at a problem, you really did need to work within often tight, limiting constraints. I wasn't employed in the field, just a serious hobbyist finding opportunities to interface. Now of course a medium PIC would do pretty much all I had the computers do, but learning BASIC line by line, example by example is never time wasted. The Tandy Basic Programming Guide was very easy to follow as it gave examples of usage. Bringing computing to the masses from a corner shop known for CB's, batteries, styli (remember them??), remote control toys and components is some achievement.....! Tandy (Radio Shack) will always be held in high regard in many eyes.

I often thought that if I'd joined the User Club my life could have taken a different path (although no regrets with mine so far). This was all so new that you didn't need formal qualifications to get a job, just ability or the capability to speak geek to the boss. Imagine then, all new to everyone, finding a teenager that would connect a fancy, new technology fangled machine, to whatever you needed it connected to and program it... Now you need to hold a degree to be pretty much anything If I'd joined I would have been connecting with people from all walks of life with an interest in computing, many professionals and business owners. However the club was in the shop meaning serious travel time and expense for me to get there. I did become good friends with the shop manager (and pretty much every Tandy manager I've ever met too) and a few years later bumped into him locally. We met for a drink and he brought some engineer along (much, much older than we were, possibly apprenticed to Edison) and he told me he was now in some start up and would like to put some work my way if interested. This engineer started to veto the idea as he was thee guy in charge of all engineering. My friend whom was very senior to him (in management) shut him down by saying "this guy has probably forgotten more about computers in the three years I've known him than you will ever be capable of learning". I was quite flattered, especially as we both knew it to be untrue. He was just sick to the back teeth of the engineer's negativity and general disdain of all things digital... I wish to clarify that I don't consider myself a programmer, and clearly I'm no genius behind a keyboard, but if my path had changed forty odd years ago who knows....

When the BBC decided to get into the game I thought why? What could they bring to the table? All transmissions were analogue and in comms KiloStream was thee talk especially as Megastream was for seriously rich companies (hmm, banks had them...) I wasn't aware of an Open University course requiring a Beeb (maybe there was?). Of course the government was quite cleverly backing the idea and nobody can deny putting a computer into most schools was a great investment in the UK's future, even if not an expected Zilog based machine (BBC expected a Z80 based machine with CP/M capabilities).

The Beeb certainly changed Acorn's future. I did toy with the idea of an Atom which I thought quite ugly compared to an Oric (name borrowed from Blake's 7), both running 6502, but my next machine was another Z-80, the Amstrad CPC-64, which eventually ran the lighting in a nite-club. A colleague did buy a Beeb around the same time though (Rumbelow's I think) and we would often compare them.

It would be quite unfair to just compare the two chips on the "numbers", as many other factors are more relevant to respective capabilities, but we settled (many years and beers later) on although the 6502 ran faster in theory, practically there was little difference, but the Z80 is easier to interface.

If you are ever in a quiet pub, and wish it to be a riotous pub, bring the following up in no particular order for discussion:-

Best Bond (Brosnan of course)
Best looking in ABBA
Best processor / computer
Best Rock song

Interesting, to me anyway, is that the Z80 is still going strong especially in the embedded world. I believe TI use them in their graphical calculators.

Mid 80's I bought a TRS-80 Pocket Computer which in reality had nothing to do with the TRS-80 lineage being rebadged Sharp/Casio. This could be programmed in BASIC and I found it extremely useful. I had a "database" I used when pricing jobs.

Clearly, like many others I'm sure, Tandy holds a special place in my history and I'm sure Beeb, Spectrum and C64 users feel similar. It is a bit of a shame that few today will experience the same thrills as we did, exploring BASIC in uncharted waters..

Thinking on my earlier post, I think I'm looking at using the TRS-80 much like FAD. It will gather the data from a PIC (or whatever) for whatever purpose I come up with. Really open to any ideas though as to what I can use it for and will document.

Regards

[steve001]

Hi Iain

Cooor that brings back some memories.. never had a TRS80 but had a ZX81(kit form) and a Beeb in later years.
I can remember saving up from my paper rounds and milk round and buying a Tandy 4 colour Pen Printer and interfacing it to my Beeb, and my then mates ripping the aboulte, p~%s at the 12 characters a second print speed i didn't care as i had at the time made my own printer lead and was so chuffed and i had 4 colours where they had just the one, black ! from a thermal printer.

I was a member of the Bradford Tandy Club @ Foster Square for a couple of years but i don't remember doing any computer related things it was mainly audio amplifiers, audio mixers.

I still have my Beeb its in the loft somewhere but i am wary of switching it on can envisage it bowing sky high as the PSU caps fail.

Steve

[chipfryer27]

Hi Steve

The ZX80 came out around March 1980 (I think) but it never really caught my eye despite the adverts implying it was equally at home balancing your books or running a power station. Wonder how many orders Sinclair got from British Nuclear Fuels It had a membrane keypad like my Mk14 (hmm...) and what I thought of as a poor method of entering commands. I personally thought it was a cheap entry level affair especially as instead of typing in your command, much like a calculator you used a combination of keys to enter "Print" for example. It did however get very fair reviews so what did I know... I'm sure many cut their teeth on one and have fond memories of the screen flickering every time you typed (seen as a mark that it was working).

I always liked the look of the ZX81 though and I'm not surprised it won a design award. Had I not bought the TRS-80 in 1980 I might well have gone for the ZX81 when it came out the following year, and like you would have gone for the kit version. I don't think the ZX81 ever had the chance to really shine in the hobby/electronics market as a year later the Spectrum was on the scene and soon dominated the home market. The ZX81 to me, was capable and importantly cheap enough to interface with and if it all went wrong there were only four (?) chips to replace

Great work in getting that Tandy printing with your BBC, I'd be quite chuffed at that too and would no doubt have been asking if "the mates" only watched B&W movies / TV too.....

I don't ever remember any Tandy Clubs other than the TRS-80 Users Group that met in the store. Maybe our branches were in towns too small to have a worthwhile capture area to offer?

Would you believe the first printer I actually bought would have been very late 80's or perhaps in the 90's? It's in the loft but I can't remember the make, uses a typewriter ribbon and has tractor-feeds too. You can either insert single sheets of "proper" paper or feed in a box of punched edge paper.

You need to get up into the loft as that Beeb is pining for you It won't take long to visually inspect those capacitors and I can assure you that seeing it come back to life will be very well worth the effort.

Regards

[steve001]

My Dad got me the kit form ZX81 as i was starting to get interested in electronics, i dont member how many chips it had might have been 6 definitely some 40 pins and some 14 / 16 pins loads of resistors, diode and a handful of capacitors the power supply brick was pre assembled. I do rember getting a 16 K Ram pack and having to hold it in place with blu-tack because it wobbled and then crashed.

Yes i was chuffed to bit's when i got it printing and draw a part graph - the pens started to tun out ..

Thinking about it, the tandy club was probably a clever marketing thing as i can remember using there kits that had components mounted under a cardboard sheet with springs and you connected wires to these.

The guy that ran the club was good had an interest in teaching and making it fun, and did come to our school on the odd occasion to the electronics club this is how i got to know about the tandy club

I still have a tractor printer like you mention with my beeb stuff a brother M1009 i only know as i did have a wacky idea of trying to print to it with a micro

yes i need to get back in the loft, i have seen cap kits on the beeb forms (zerodot.org) for only a tenner or so

I have a lot of things on the go at the moment since starting a new job in march but definitely on the list i think


Steve

[chipfryer27]

Hi

Similarly, my parents got me the Mk14, which had a dozen or so chips but didn't come with any PSU....However it did come with good advice to not power it until the next day after soldering it all together. This was to allow your brain a break and was good advice, well to a 14yr old..

I had no suitable mains supply so a PP9 battery was pressed into service and when the little 7-segment, 8-digit display came on I was a happy kid indeed. Clearly batteries were a temporary solution so as soon as I could afford it, off I went to Marshall's in Glasgow, thee component supplier, for bits to build my own supply, which was housed in a not too great wooden box alongside the Mk14 (I make no claims about my carpentry skills although at college I did build a crossbow instead of the electronics I was supposed to be doing. We were learning about "computers" and as the lecturer had already established I had done far more than the course entailed, it was better to let me do my own thing than annoy others with my new Walkman). I later soldered leads from the PCB edge connector to a series of terminal strips as a way to connect it to the world, but as I had no way to store any program it was mainly a learning experience. I wasn't too impressed with the included manual, it wasn't very clear to a complete novice and I was soon up at Smith's, the best bookshop by far, ordering up "The Complete Guide to SC/MP Programming" which cost me about £14 for forty pages of A4 spirally bound, a lot of money then but very well worth it as it explained everything about the chip and how to use it (all machine code).

I remember well the ZX81 (and Spectrum to a lesser extent) expansion pack problems and as you mention, BluTack was the official fix...

I built many a Tandy kit too, the one I used most was the signal generator / tracer. It injected a tone you could then follow through a circuit. Worked well except the case screws kept coming undone, so they got glued in place

Regards

[Steve-Matrix]

Thanks for the interesting thread.

My favourite memory of early micros was writing a music sequencer in assembly on a BBC and interfacing it with a drum machine. I used different on-screen characters to represent different pulse lengths and directly read the video memory, outputting these through 4 channels on one of the Beeb's ports. I took the drum machine apart and fed these 4 outputs directly into the pad sensors to mimic different strengths of pad hit.

The kit has all gone now, but I may still have some cassette tapes of the music I made with it.

[chipfryer27]

Hi Steve

That sounds a very cool project indeed.

I may still have some cassette tapes of the music I made with it

You know you need to post examples I thought you were more Cozy Powell than Kraftwerk...

I wonder what percentage of computer users at the time interfaced their machines to something, to those that either enjoyed programming or just saw them as a way to play a game?

Of course then, just creating a PCB was a challenge. No KiCAD or the like, so anything that was built was in itself an achievement! For me with my limited resources, creating a PCB would require drawing tracks with a permanent marker or using transfers, after which a very hit-or-miss dunk in a bath of acid before hand drilling.... It was much, much easier to just use Veroboard and not try too much to use the strips as tracks, instead just as a means to mount the components and then "rat's nest" connections.

I found a board I built to interface a machine to a telephone line. It was probably a Commodore PC1 (8088 chip??). The board needed to detect when the phone was rininging and answer, detect touch-tones entered by caller and pass to computer, and via text-to-speech conversion output the generated speech to the caller. Budget was a whopping "nothing". Well none to speak of.

The interface consisted of two modules. One detected the ringing and would answer/clear the call, detect the tones and interface with the computer, and the other was a 2-wire / 4-wire converter which as the name suggests takes a 2-wire line and turns it into a 4-wire circuit (tx/rx) and vice-versa.

Veroboard and rat's nest was the way to go. The interface worked fine and was very much a success. Unfortunately the PC1 had no hard drive but you could create a RAM drive and this was used to good effect. The only real issue with the device was the incoming supply, which in the city centre was quite noisy and prone to dips. This of course messed the computer up requiring a reboot etc.


Interface board with rat's nest:-

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The large relay dominating the above was no doubt scavenged and would just energise when the ringer was active (incoming call). This signalled to the computer a call was present and the small relay to the right was used to answer / disconnect.


Tone Decoder:-

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That Teltone chip accepted DTMF tones and converted them to a BCD output, and was very expensive. I think it cost around seven pounds....


Address Decoding

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It looks like I've separated the data bus to the address bus and other lines. Looks like I'm only decoding the LSB's of the address and every bus line would go to a tri-state buffer. I don't have the 2W/4W converter though, but it was just really used to interface the speaker connections/tone decoder.

I hasten to add that now I can create boards by chemical means, by CNC or by just sending off the Gerbers

Regards