Differences between model 1, 3 and 4

[Abmvk]

I am searching online, but most I find is rather high level. I am looking for details, as much as possible. For example, I just found out that the disk basic of the model 1 has the SET and RESET command, but the disc basic of the model 4 does not. And (my) model 4 has no BASIC in ROM, where the model 1 does.

But well, really any source of detailed comparisons would be appreciated!

 

[TRS-80.com]

I suspect the best resource would be to just look at the Radio Shack catalogs back in the day.

An archive of RadioShack Catalogs (1939-2011)

Flip-through every RadioShack electronics & computer catalog. These catalogs include vintage electronics, stereos, speakers, CB radios, tube radios, computers, communication equipment, electronic test equipment, gadgets, technology & more!

radioshackcatalogs.com

 

[Eudimorphodon]

And (my) model 4 has no BASIC in ROM, where the model 1 does.

Do you have a Model 4P? Regular desktop Model 4s have Model III basic in ROM, just hold down the BREAK key when you turn it on. (Or boot a Model III DOS.)

Short version of the response to this question: a Model 4 booted into a Model 4 DOS is a *completely* different computer from the Model I and III. (Those two are mostly alike.)

 

[Abmvk]

I have a model 4, not the portable, as far as I can determine. And it doesn't boot to Basic, even when I hold down the BREAK key. At least, I don't think so. Minutes after my initial post the computer was producing white smoke, so there is some repairing to do first.

 

[ldkraemer]

That was likely the Square RIFA Cap(s) blowing on the Power Supply.
They should be replaced ASAP.

If it's a TANDY Power Supply versus ASTEC, you need to remove it and check the
Row of Pins for little rings around each pin. Then re-flow the solder for each pin with
some KESTER 63/37 Solder. That will fix the Tandy Power Supply.


Larry

 

[gp2000]

All Model 4's except the portable 4P have BASIC in ROM. If your Model 4 wasn't going into ROM BASIC when you hold down the BREAK key on boot there are only a few possibilities.

• You actually have a 4P (if the diskettes are oriented vertically it's a 4P). Or show us a picture.
• The BREAK key is broken.
• You didn't hold down the BREAK key before powering on or resetting the machine.
• Something quite unusual is going on.

The Model 4 wikipedia page shows the difference between the models pretty well:
https://en.wikipedia.org/wiki/TRS-80_Model_4

 

[kiwisincebirth]

This wikipedia page has a good overview of changes from Model 1 to 3

TRS-80 - Wikipedia

en.wikipedia.org

Apart from the obvious form factor change and other functional improvements, the main differences from a hardware perspective (IMHO) were the move memory mapped IO (e.g. Disk Controller) from $37Ex into IO address space, which made way for an expanded 14KB ROM. If you search there are many sources of the memory and IO maps, which can be compared. I think this was the biggest areas of incompatibility requiring minor software changes.

 

[Abmvk]

Some update if you are interested

I had the problem with the RIFA solved by the specialists at our local Home Computer Museum ( https://www.homecomputermuseum.nl/#intro ), they also cleaned the drives and helped me with a NewDos/80 boot disk.

I am afraid there still is a problem with the :0 drive as the bootdisk was corrupted within a day. But what I did find out in the meanwhile is that the Model 3 BASIC is available in ROM. So that is one mystery solved, I just didn't boot the right way.

Now finding out if there is something wrong with drive :0 or I have had bad luck with the boot disk is the next step.

While I am at that, maybe another thing. The little square indicator below the reset button says it is a 64K device, I until now could only find 32K. Is it possible there still is 64K in there but I am looking wrong, or is that indicator just fake?

 

[Eudimorphodon]

While I am at that, maybe another thing. The little square indicator below the reset button says it is a 64K device, I until now could only find 32K. Is it possible there still is 64K in there but I am looking wrong, or is that indicator just fake?

The Model III came in 4K (very rare), 16K, 32K, and 48k, the Model 4 came in 16K (no disks), 64K, and 128K.

 

[Abmvk]

That means my finding only 32K in my model 4 its impossible. Hmm, thanks, I will try another way to test.

 

[Eudimorphodon]

That means my finding only 32K in my model 4 its impossible. Hmm, thanks, I will try another way to test.

What do you mean “find” 32K? If you’re in the Model III basic “PRINT MEM” should give you a number about 1K less than 48K, which is correct in that mode because the lowest 16K of the memory map is filled with 14K of BASIC ROMs, the video memory, and the memory mapped keyboard.

If you’re trying to test memory by PEEK and POKE-ing an important thing you have to remember is in Model III BASIC all addresses above the 32K mark are negative numbers, because the BASIC only supports signed integers.

TRS-80 Tips and Tricks – Level II Tips and Tricks – Ira Goldklang's TRS-80 Revived Site

 

[pebecker]

The Model III came in 4K (very rare), 16K, 32K, and 48k, the Model 4 came in 16K (no disks), 64K, and 128K.

I had a Model III 4K level 1 machine back in the day. serial # 218, I think. I later converted it to a model 4, but requested that the service center send the original motherboard back to me, which they did. Soon I hope to have that machine back at my house, and I also have an empty model 4 case. The plan is to move the 4 guts into the 4 case and put the original 4K motherboard into its original case.

 

[Torch]

So what were the advantages of a DT-1 compared to a Model III level 1 at the same $699 price (plus $79 for the RS232)?
Was the 80 column display of a dumb terminal more important than buying a real computer?

 

[Eudimorphodon]

So what were the advantages of a DT-1 compared to a Model III level 1 at the same $699 price (plus $79 for the RS232)?
Was the 80 column display of a dumb terminal more important than buying a real computer?

They're not really comparable products? While sure, in theory at least, you might have been able to write a terminal program to fit into a 4K RAM Level I BASIC Model III (which you'd have to CLOAD at 250 baud every time you wanted to go online) that obviously wouldn't have been a very practical solution the office environments where you'd be using a DT-1 to talk to a Model 16 or mainframe or whatever. And yes, the DT-1 has an 80x24 screen layout, which by 1982 (when it came out) was considered the standard for the sort of environments it was intended for. The DT-1 also supports attributes like reverse video, half-bright, and underline, like you'd expect on a "real" terminal, although I guess if we were going to be mean about it the terminal emulations it supports aren't really very good at using attributes to their full effect. (The DT-1 is one of those terminals where turning an attribute on or off takes a "character space" out of the screen, so you effectively can't have, say, a reverse video cell, directly next to a plain one.)

I mean, sure, if a 64x16 terminal is adequate you could buy the Model III instead, but I suspect you'll at least have to buy the 16K Level II one to actually be able to find a terminal program to run on it.

 

[cjs]

So what were the advantages of a DT-1

First, the DT-1 has certain hardware essential to a terminal that you'd need to add to the model I, such as a serial port. (And printer port, if you need local printing.)

Second, a lot of stuff is designed for an 80x24 display and won't work so well on 64x16. Perhaps even more common is wanting lower case, which the DT-1 has and the Model I does not (absent hardware modifications).

But perhaps even more annoying, the Model I's keyboard was missing a number of keys that were often pretty important for use of remote systems. The Ctrl key is the biggie there (imagine using a remote CP/M system without being able to type even Ctrl-C), but Esc is another one commonly wanted, and printing characters from '[\]^_`{|}~' (all missing on the Model I) are also often enough wanted.

This is all fixable, since the Model I has a software-scanned keyboard; the first obvious change would be to make the down arrow into a Ctrl key. Whether you want up arrow to be changed to Tab depends on how happy your users are with learning to type Ctrl-I instead; I might use up arrow as a modifier key to give us keystrokes that can give the above printing chars. (Or Esc, depending on how much I find the substitute Ctrl-] annoying.) But you still end up with the issue that you'll have to have a guide somewhere to what's been changed, users have to remember these, etc.

But where you're going to get that terminal software is an open question, especially to run on a 4K Level 1 machine. I'm not even sure if you can load machine-language programs on Level 1 machines.

 

[Eudimorphodon]

I'm not even sure if you can load machine-language programs on Level 1 machines.

There’s not a proper SYSTEM or CLOADM command, but there is a backdoor for loading M/L programs via CLOAD. Tandy’s T-BUG and EDTASM developer tools came with both Level I and Level II versions in the box.

There were a handful of M/L games for Level I, but other than the assembler and debugger I don’t know of anything else. A terminal program would have been particularly weird given Level I Model Is were electrically incompatible with the expansion interface. (A +5v output was trace cut and turned into a ground when Radio Shack installed the Level II upgrade.) Obviously not a problem with a III, but still, where are you going to buy a Level I with an RS-232 board installed?

 

[cjs]

but there is a backdoor for loading M/L programs via CLOAD

Ah, this one. I'd forgotten about that.

A terminal program would have been particularly weird given Level I Model Is were electrically incompatible with the expansion interface.

Well, it was the 1970s. Buying things is for losers: of course you build your own RS-232 interface and, while you're at it, terminal program.

 

[Torch]

I started off with a normal 16K Model III, but I guess I never realized how limited the Level I version was. I knew they were in the catalog, but never saw one in a store.
I was about 13 when I saved up and bought the tech ref. manual and RS232 board from my local RCS. Then they let me buy a DCM1 for $40 (I think it was a return) and the Vidtex software for $15...that center was good to me. That was enough to get me on Compuserve.

For some reason I thought Vidtex on cassette supported Level 1. As a kid, I thought if I had a small business, I'd rather give my secretary a Level 1 Model III because it could be used as a terminal and be expanded with software and hardware as time went on.

So what did the $300 Model III upgrade kit consist of? My tech manual mentions nothing about the Level I version. It does state that the first RAM bank is the only one that can support 4K, so I always assumed the upgrade was nothing more than a ROM and RAM swap.

 

[Eudimorphodon]

Well, it was the 1970s. Buying things is for losers: of course you build your own RS-232 interface and, while you're at it, terminal program.

People did used to write simple terminal programs to bit-bang half duplex serial using the TRS-80’s serial port and, with the help of some external hardware to handle level conversion, use that to drive 110/300 baud modems, you can find articles on that in 80 Micro and the like so… sure, why not, you could probably do that with a Level I TRS-80. But per the original question, obviously this is not the kind of performance or application nearly anyone who was in the market for a DT-1 would be satisfied with.

FWIW, there were a couple modems sold that contained a UART and directly connected to the Model I; I actually had one of these sold by a company called Microconnection. Here’s a review mentioning it:

80 Microcomputing Magazine September 1981 : Free Download, Borrow, and Streaming : Internet Archive

archive.org

I suppose it’s possible they sold a Level I tape for it, or some fiend wrote something for a modem like this (bought or homemade), which would at least perform slightly better than the cassette port, but… again, not really applicable to a Model III.

 

[Eudimorphodon]

For some reason I thought Vidtex on cassette supported Level 1

Maybe it supported the 4K standard BASIC CoCo.