TRS-80 Model I info (RE: MSX, TRS-80, Colour Genie, etc.)

From: Kai Kaltenbach <kaikal_at_MICROSOFT.com>
Date: Wed Jun 25 18:40:01 1997

The Model I originally shipped without a numeric keypad. To the right
of the main keyboard was a rectangular keypad-size plaque reading "Radio
Shack TRS-80 Micro Computer System". The numeric keypad was added to
later models, and was available as a retrofit kit for around $50. With
the numeric keypad installed, the nameplate was moved to a horizontal
plaque above the keyboard.

The TRS-80 Model I lineage includes:

Model I, 4K, Level I BASIC
- This is a 3-piece system with the computer in the keyboard. It
includes the system keyboard/cpu, monitor, tape drive (actually a
rebadged regular Radio Shack portable cassette deck with no
modifications), and power supply brick. Level I BASIC is similar to
Tiny BASIC. I still have my Level I BASIC reference manual.

Model I, 16K, Level II BASIC
- The 16K and Level II upgrades went together. 16K is the maximum Model
I memory in the system unit (8x 4116 DRAMs). Level II BASIC is similar
to Microsoft BASIC/80 with functions added for things like the TRS-80's
128x48 memory-mapped monochrome graphics. Level II also added a
keyboard debounce routine--Level I machines were very difficult for
typists.

Other Upgrades:

- Expansion Interface
Matching silver color, acts as a monitor stand, connects to system unit
via ribbon cable. Contains dual floppy controller (WD chip), sockets
for an additional 32K (2 banks of 4116 DRAMs) for a system maximum of
48K, and a parallel connection. 16K ROM BASIC occupied the remainder of
the address space. The expansion interface also contains a card bay for
an RS-232 interface.

- RS-232 interface board
For expansion interface.

- Floppy drives
Single-sided single-density, approx. 90KB free space.

- Lower case upgrade
Provides lower case capability.

- Numeric keypad retrofit
As discussed above

Known TRS-80 Model I problems:

- Unreliable cassette interface. Radio Shack later released a
modification that improved this somewhat. The best option is a
third-party unit called the Data Dubber by Microperipheral Corporation
(I worked there!) that went in between the system unit and cassette and
squared the wave.

- Wonky, unbuffered connection to Expansion Interface. This went
through various modifications, and some cables you'll see have big
buffer boxes in the middle. Later Expansion Interfaces had built-in
buffering. Some bought third-party expansion interface clones from Lobo
and others. Be very careful if you get an Expansion Interface without a
cable. It might need the buffered cable, and it would be a pain to
manufacture.

- Bad data separator chip. The stock data separator was unreliable.
Most people replaced theirs with a third-party improvement such as
Percom's.

- Unreliable connection for the Expansion Interface-mounted RS-232
board. This board slipped over vertical post connections and never made
good contact. Most folks used third-party alternatives that worked off
the cassette port.

Kai


> ----------
> From: Mr. Self Destruct
> Reply To: classiccmp_at_u.washington.edu
> Sent: Wednesday, June 25, 1997 4:14 PM
> To: Discussion re-collecting of classic computers
> Subject: Re: MSX, TRS-80, Colour Genie, etc.
>
>
> On Wed, 25 Jun 1997, Scott Walde wrote:
>
> > No. They were originally known (and labelled) as the TRS-80
> Microcomputer
> > System. They later became known as the model 1 (Although I don't
> think
> > they were ever labelled as such.)
> >
>
> Were there two different Model 1's? I have seen pictures of Model 1's
> that don't look like my Model 1. (i.e. no numeric keypad)
>
> Les
> more_at_crazy.rutgers.edu
>
>
>
Received on Wed Jun 25 1997 - 18:40:01 BST