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

From: Ward Griffiths and/or Lisa Rogers <>
Date: Wed Jun 25 23:07:56 1997

On Wed, 25 Jun 1997, Kai Kaltenbach wrote:

> 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.

Level I BASIC _was_ Tiny BASIC.

> Model I, 16K, Level II BASIC
> - The 16K and Level II upgrades went together. 16K is the maximum Model

They wre available separately -- but a 4k Level II machine only left
about 1800 bytes of free RAM -- not a pretty sight (And yes, I've seen it!)

> 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

Amazing, though, how Big Five could use those graphics for the most
amazing video games (and produce sound from the cassette port to match)
-- it took the PC a couple of years to match it.

> keyboard debounce routine--Level I machines were very difficult for
> typists.

Actually, the keybounce problem existed with Level II -- the keybounce
fix was a tape to read originally into a Level II box -- there was never
a fix for Level I (my own system the keybounce always came back -- I never
used the tape, it ate a K of RAM I needed -- when I made the mistake of
turning the keyboard upside down and dumping out the cigarette ashes ,
while they were there, apparently it smoothed the keyswitch operation
adequately). There was a second release of Level II BASIC that included
the debouncer in the 12K ROM.

> 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.

Dennis Kitsz did once publish an upgrade to 48k that could be done in a
keyboard without the EI. I have no idea how many others built it, but I
never had a problem with the alleged memory speed problems from the EI
cable. Jerry Pournelle's gripes are another story.

> - RS-232 interface board > For expansion interface.

Worked better than an Apple serial card from the era.

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

Geez, I remember spending $39.95 for my first 10-pack of SSSD 35-track
disks. Amazingly, I years later formatted one of them in a Tandy 2000
DSQD drive (call it five years later) with full verify and got two bad
tracks. Yeah, I should have hung onto the disk, put some data onto it,
and tried to read that data a year later. But I was about to throw away
the disk anyway, since it had shown errors on a Model 3.

> - Lower case upgrade
> Provides lower case capability.

I _still_ don't understand that trade-off between cost and utility. The
decision makers were gone before I joined the company in '80.

> 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.

It was more reliable than the cassette interfaces for the Apple or the Pet
ot the Atari. _All_ cassette interfaces are unreliable. How many people
used the cassette interface on an Apple for more than a week before they
gave up and got a disk drive? How many people used the cassette interface
on the Atari 400/800 for more than a day? Some TRS-80 users never felt
the need: it was not as unreliable as most of the competition. Many Color
Computer users noticed how much faster their cassette transfers were than
Commodore disk drives that they didn't upgrade until OS-9 showed up and
they _really_ needed disk drives.

> - 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.

Can't make excuses for this technically myself. That unbuffered cable
carrying RAM signals was flat-out stupid. But remember that when the
first machines were designed that the company (always retail driven) had
_no_ idea that the damned things would sell, it was an experiment. Hell,
Apple and Commodore had been advertising all year, and hadn't delivered
more than a few eval and review units when Tandy announced the TRS-80
Microcomputer System on 3 Aug 77 with 5,000 units already in the
warehouses -- idea was, since they didn't know if it would work, they had
5,000 stores -- if the silly things didn't move they'd figure out a way
to use them.

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

The one Percom used came out after the design was final.

> - 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.

_Nothing_ was reliable in the Expansion Interface, ever. Not even the
clock. And the Model III came out about the time most of the problems
were solvable. Many companies phase out upgrades of systems that have
been superceded -- when's the last time MicroSlough actually fixed one of
the many problems that still exist in Windows 3.1?
Ward Griffiths
"America is at that awkward stage.  It's too late to work within 
the system, but too early to shoot the bastards." --Claire Wolfe
Received on Wed Jun 25 1997 - 23:07:56 BST

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