Trs-80 In My Hands! Yay!

[Theory5]

Hello all! I havent been posting for a couple of weeks now, so I thought Id say hello.

This month has been awsome, I got vista, I got to go to a Dropkick Murphy's concert, and I found a TRS-80 model III microcomputer!

so Im here to talk about the TRS. I found it today 9/15 it has been sprinkling all day. Me and my dad were coming back from dropping off my friend at his house, when suddenly, I saw an old computer sitting out on the wet grass in the rain waiting for trash day. I had my dad turn the car around, and we stopped and looked at it and put it in the car! Now Im in the middle of cleaning it and ridding it of various, bugs, dirt, and water! I finished what looked very little like a motherboard (the only resemblance was that it seemed like everything hooked up to it) and the 2 boards behind it, I guess one of them had a processor on it.

my dad warned me to be very carful about touching the moniter parts, cause we dont know when it was last plugged in.

But Please, can you tell me all of what you guys know about the TRS-80 model 3?

[Janus]

One thing I remember is that it used a

Zilog Z-80 processor:

 

Zilog Z80 8-Bit Microprocessor

[Theory5]

One thing I remember is that it used a

Zilog Z-80 processor:

 

Zilog Z80 8-Bit Microprocessor

 

ooooh, I think that was the one with the blue sticker on it.

[Buffy]

Oh, my. A Trash-80! That's a classic!

 

The model 3 was the later version with the monitor and floppies built-in, so its not as classic as the original keyboard-only model that hooked into your TV set and required a cassette player to (try to) store data.

 

I am pretty sure it had the same 160k floppies that were on the original Apple ][ and IBM PC, which are very difficult to find, and it only ran a custom version of CPM that only ran on the 80 and not on anything else (ROM dependencies). It should have Basic in ROM though, so you should be able to fire it up and do some interesting things even if you can't find a copy of the OS (which may in fact be findable some place out there on the Internet).

 

Antiquing,

Buffy

[Theory5]

Oh, my. A Trash-80! That's a classic!

 

The model 3 was the later version with the monitor and floppies built-in, so its not as classic as the original keyboard-only model that hooked into your TV set and required a cassette player to (try to) store data.

 

I am pretty sure it had the same 160k floppies that were on the original Apple ][ and IBM PC, which are very difficult to find, and it only ran a custom version of CPM that only ran on the 80 and not on anything else (ROM dependencies). It should have Basic in ROM though, so you should be able to fire it up and do some interesting things even if you can't find a copy of the OS (which may in fact be findable some place out there on the Internet).

 

Antiquing,

Buffy

 

yea i heard about the OS, you run it from the floppy, correct? but even if I could find a copy I would have to buy it, cause i dont think this computer is fitted for a 160k floppy drive :-P

so you say I can run basic on it? cool. does it have any sort of graphic interface or is it just all text, do you know?

oh, also underneath it it has 2 things that look like they might connect stuff, my dad said it could hook to a printer, but what is the 2nd connector for?

[Janus]

Here, Maybe these will help:

 

TRS-80 III manuals

[CraigD]

According to the wiki article, The model III should be very similar to the model I, with which I was once very familiar. Other TRS models are much different from the model I.

 

Practically, the machine is stand alone, powers up to a BASIC command line that will allow you to hand-enter a program and run it. It has audio in and mike out jacks that allow it to save programs and files to 1/4” cassette tape, so you can save and reload programs. I don’t recall if it was built-in or a small external box, but an RF modulator allowed the machine to be connected to any TV that could tune channel 2 or 3 (A special monitor for it was available and very common, because, I recall, it was cheaper than a TV).

 

As with many basic interpreters of its era, entering a line starting with a number inserts it into the current program, while entering command(s) not preceeded by a number executes them directly. The RUN command runs the current program.

 

The BASIC has simple commands to do most useful things, including pixel-at-a-time or line graphics, and polling the keyboard, making it possible to produce fairly amusing programs such as video games in very short time. At very least, entering direct commands such as PRINT 2*3^4+5 (or, abbreviating the PRINT keyword, ? 1+2+3) make it a pretty decent, though low-precision, calculator, with lots of scratch memory (eg: A=1+2 : B= A*3: ? A,

 

It has, as I recall, a “mike switch” jack that will control the start and stop of a Radio Shack cassette tape deck of its era (which had a special jack for this function) but can’t switch from play to rewind and fast forward to truly control the tape to access files under computer control. So to do any sort of serious data management, you must write program instructing the user to rewind and ff the tape, press RETURN, press the play or play+record button, and press RETURN again. If the user messes up, files on tape can be accidentally overwritten. As cassette tapes have a mechanical punch-out that can make them read only (like the slide hole on a 3.5” floppy disk), important programs can be kept on read-only cassette tapes.

 

Practically everything on the TRS-80 is mapped to fixed locations in memory, so its very easy to write assembly language programs for it. Radio Shack made a pretty decent assembly language compiler for it, which I still have the documentation for, being an excellent Z80 machine language reference which I’ve used to hand-assemble on other Z80-based machines.

 

TRS-80’s can control disk drives, but these were much less common than cassette tapes, and, I recall, inconvenient to control and program. The Model 2 had a built in 8” floppy disk drive, but, as mentioned above, was almost a completely different machine, and less easy to program.

 

Unless you know someone who has diligently re-written all their cassette or floppy TRS-80 programs and data every year or so (which, with the internet (especially ebay), may not be as unlikely as it sound), you’ll likely be unable to find loadable programs for it. You might have better luck finding old magazines with printed program listing, and entering them by hand. The real fun of a TRS-80 is to just begin programming it from scratch. It may take a bit of searching, but you should be able to find at least a photocopy of its (very well-written) user manual, which explains about everything practical you need to know about it.

 

By modern standards, the machine is very slow, low-resolution, and for all intents and purposes, unnetworkable, but it’s quite capable of doing a lot of useful, interesting, and just plain fun things.

[TheBigDog]

I had a friend who had a TRS-80. The syntax of the BASIC was different from my Atari 800, which was different from the PET (Commodore) computers that we had at school, which was different from the Apple II computer that my other friend had. The TRS-80 had an 80x24 character screen, where all of its competitors had 40 character wide screens. It did not support graphics, only characters. All of its games were executed my using characters to form bigger pictures and then moving them around the screen like connected blocks. I remember playing Asteroids that way on the TRS - very cool in 1981! It was also only a black and white display. The extra wide screen display was its selling point. The reason it was only black and white was because of the native resolution and the pixels needed to support fonts 80 characters wide on a TV screen.

 

It is a cool old machine. If you get it running send in a picture for the scavenger hunt!

 

Bill

[CraigD]

The TRS-80 had an 80x24 character screen, where all of its competitors had 40 character wide screens. It did not support graphics, only characters.

My memory of TRS-80s is of very long ago, and difficult to separate from every other machine of that era I could get my hands on, so I googled a bit to confirm it.

The TRS-80 model I (and, I believe, the III, though I’ve never layed hands on the latter) has 16 lines of 32 characters. Everyone I ever touched had a BASIC command (perhaps a POKE, or a special keyword, I’m uncertain) that would switch it to 16 lines of 64 characters. If you kept it in 16x32, you could draw to an invisible display, then switch it quickly to become active, making for a smoother look. Also, staying in the lower resolution kept the pixel more square, and reduced graphics rendering time.

 

I’ve forgotten the exact size of each print position, but you could turn on and off individual pixels simply by POKEing single bytes into its fixed graphics memory. If you PEEKed the location first, you could use PRINT to throw up some text, then put lines around and through it.

 

The Z80 processor excelled at “block moves”, having instructions specially for it, so short machine language programs (like many BASICs, the TRS’s had a USR() function to return the location of a string in memory, and a USR command to transfer control to that location, so you could write short machine language programs using string variables and the CHR$() function, and invoke them in code) to all or part of the display a single pixel in any direction were common, and easy to find in various “advanced graphics” books and articles. Rendering a pretty graphic, then shifting it around while undrawing and redrawing a small cross in the middle of the screen, while using the keys to point and shoot, made it possible to make pretty nifty video games without a lot of effort. It was possible to make side-scrolling games using the same approach, drawing a column of 1 to 8 pixels at a time on the screen edge, then shift everything sideways, but the machine had so little memory – some 16K, some 32, as I recall – that you couldn’t have anything long or interesting to explore this way, even keeping the big drawing to a minimum number of simple lines.

 

The TRS-80 may well be what caused me to be where I am today. I encountered one in my college’s Math department when I was a Fine Arts major, and was enthralled. I adapted an old “lunar landing simulator” I’d written years earlier on a teletype terminal system to allow you to control a “throttle” with a few keys (up, down and one key for 0, 10, … 100%), and found it very amusing. Leaving it running, people quickly made tape copies of it, and before long a bunch of Math and science majors hunted me down and encouraged me to stop spending my spare time making jewelry (including my major source of income, custom 25 mm fantasy miniatures for obsessed gamers) and instead programming TRS-80s and Apple IIs. I switched my major to Math, my source of income to tutoring and programming, graduated, taught, and eventually wound up programming for a living. Had it not been for that first TRS-80, with its “anybody (who knows a little BASIC) can sit down and begin programming” simplicity and friendliness, I might well have stayed an Art major, and be doing something completely different today than working in IT - something likely involving selling Appalachian art to tourists at craft fairs and state parks, or teaching folk to do this or teach folk to do this.

[Theory5]

Sweet, a bit later today Im going to connect the moniter back to the rest of it and see if I can get it running ( I will be doing this outside or in the garage, where i have the TRS-80 already. and I will have a fire extinguisher handy :-). I only know Liberty Basic but Im willing to learn. Heh, I doubt I can find a cassette player for it. But it does have internal memory right? so I can say write a little program on it then shut off the computer and go back on later? or do I need the cassette player for it?

 

Think Radio Shack will sell me a cassette player for it? :lol:

[CraigD]

Ah, here is a reference to TRS-80 level 2 BASIC. It’s not the excellent manual I recall having, with lots of useful examples and sample programs, but appears to cover all the keywords and functions, and should be enough to get anyone who knows even a little BASIC writing and running programs on the TRS-80.

 

Note that my and TBD’s recollection concerning graphics were quite inaccurate: the BASIC has a SET and RESET command that lets you draw graphics a pixel at a time, a much safer means than POKEs. My recollection about a USR() function was from another BASIC – in the TRS-80 Level 2 BASIC, the function is VARPTR(), and its easier to allocate space by DIMing a numeric array, then POKEing the program into memory there. Writing and reading data from cassette tape is a lot more difficult than I suggested – again, I was remembering another cassette-based machine’s BASIC.

[Buffy]

Here's a pretty good page on the specs for the Trash-80 Model III[ that outlines a few details mentioned above:

• Had 0, 1 or 2 5 1/4" 160k floppies, so they were optional and you could have one with none installed, meaning cassette only "memory" as was the only option with the original Model I.
  
• Had 32 or 64 col by 16 line display (32 col was a sort of a standard, the Apple ][ had it until they came out with their 80 column board which was a pricey add-on that my uncle got on his that I used to play with.
  
• Did indeed have graphics, although it was monochrome (and I bet it was 320 pixels across for graphics mode, like the IBM PC 1 that we had with a CGA monitor with FOUR colors)
  

I never played with any of these, although I knew people who had them and thought they were the best thing ever...

 

Peeking and Poking,

Buffy

[Theory5]

I plugged it in and IT WORKED! as far as I know, nothing came up on the screen but everything was definiatly on. it looked like it was looking for the OS floppy, cause the bottom floppy drive came on and spun a few times. but nothing showed on the screen. :-/

if anyone has a floppy OS for the TRS-80 model three we could work somthing out.... or maybe the computer has a problem. anyways...IT WORKS!

-theory

[CraigD]

I plugged it in and IT WORKED! as far as I know, nothing came up on the screen but everything was definiatly on. it looked like it was looking for the OS floppy, cause the bottom floppy drive came on and spun a few times. but nothing showed on the screen. :-/

That’s odd.

 

The machine should be able to function perfectly fine without using it’s drives. Its operating system consists of a few kilobytes of ROM. The only think on a floppy might be a bit of “disk operating system” - called “TRSDOS” on TRS-80s – necessary perhaps for accessing the floppy, but not simply to use the computer.

 

Try pressing the Break key – should be in the upper right corner of the keyboard. You should get an “OK” on the screen, and be able to enter something like

PRINT “HELLO, WORLD”

[Theory5]

okay I will try that

[Theory5]

nope didnt work

under the keyboard I noticed when I was cleaning it, there was somthing sticking up, a peice of plastic idk what it was for but I looked under the keyboard and there was a broken bit of board where the piece was sticking up, it had only broken one soldered connection. would that render the whole keyboard useless?

 

what does that red button do that is all the way to the right?

[CraigD]

I’ve never had a TRS-80 that wouldn’t power up to an OK (or maybe it was a READ prompt), so can’t say much about any sort of hardware problem.

 

Let’s assume there is no problem, but that you just can’t see on the screen what it’s displaying. See if you can find brightness and contrast adjustment knobs somewhere (on the separate Model I monitors, they were right on front, but per the picture in Buffy’s post, that doesn’t seem to be the case with the Model III) and play with them to get a visible picture of some text. Alternately, I recall that the machine has an internal speaker and recognizes a standard ASCII BEL, so entering

PRINT CHR$(7)

should produce a beep.