TRS-80 Model 1

TRS-80 Model 1

The Tandy TRS 80 model 1 was the first member of one of the most famous computer family. It was one of the first home computer and was launched at the same time as famous computers like the Apple II or the Commodore PET. Beside, Tandy competitors nicknamed was “Trash-80”.

The TRS-80 was developed was developed within the Radio Shack engineering group, based upon several processor chips, SC/MP, PACE, 8008, 8080 and finally the Z80.

It used a black & white TV set, made by RCA, without tuner as monitor. The earlier models use a poor basic called Basic Level 1 (the Basic and the OS fit in the 4 KB ROM!). It was replaced later with the Basic Level 2 which needed a 12 KB ROM.

To offset its poor characteristics, Tandy developed a device called Expansion Interface which brings a lot of new features : additional 16 or 32kb RAM, two tape unit connectors, a printer port, a floppy disk controller, a serial port and a real time clock.



The TRS‑80 Model I had very impressive specifications for a $399.95 computer in 1977:

a Zilog Z80 processor running at 1.77 MHz
a monochrome, uppercase-only text display, with either 64 columns by 16 rows or 32 columns by 16 rows
128 by 48 low-resolution graphics
cassette storage capable of either 250-baud (in Level I) and 500-baud (in Level II)
53-key professional keyboard
4K of memory, expandable to 16K
Expanding the Model I further required a device called an Expansion Interface. This provided:

32K of memory, for a total of 48K
a single-density floppy disk controller
a parallel printer port
an RS-232 port

When I got my unit it was Non- working

I replaced a few RAM IC’s and it booted into life.


I added a Expansion Interface for the Fred unit

The first test all RAM working


I mounted the Fred and interface unit into a case I got from Jaycar, and mounted my custom power supply.

Testing out a game on the TRS-80 Model 1

Still looking for a TRS-80 Model 1 Expansion Interface 32K

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