TRS-80 Model III

Disk III
Sprinter III
TRS-80 Model III from 1980

CPU: Z80A @ 2.03MHz
Floppy Drives: 2 full height SSDD
Display: 12" white CRT
Ports: serial, Centronics parallel, cassette, system bus, external floppy
OS: Level II BASIC in ROM, TRS-DOS 1.3
Catalog No.: 26-1062
Serial No.: 0044706
Catalog Price: $2495 System, $99 RS-232 board

This system appears to have originally been a 16KB diskless model, which was upgraded to 48KB, 2 drives and the optional RS-232 interface. The drive upgrade was the Disk III system from VR Data, also the RS-232 board.

I picked up another Model III with a Holmes Engineering VID-80 board installed, and transplanted it into this machine. The VID-80 provides memory mapping to move the Model III ROMS out of low memory, to allow CP/M to run. It also provides an 80x24 display mode, and has an additional 64KB of RAM on board. This VID-80 has another Holmes upgrade, a Sprinter III. It has a Z80B CPU and is capable of operation at 5.07MHz.

I was able to verify that the 80x24 mode works, as well as the Sprinter III switching between high and normal speeds. The machine boots up by default in 80x24 mode, but holding the '6' key while booting brings up 64x16 mode. I am unable to test CP/M because I don't have the Holmes CP/M software. If anyone has a copy of Holmes CP/M for the VID-80 or any documentation, please let me know.

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Last updated on Friday, October 28, 2022