Transam TRITON

Architecture

The Triton was an 8080-based single-board microcomputer, which could eventually be expanded to use a motherboard and various expansion boards. The hardware was all 5V TTL, and typically based on 7400 series digital electronics. The firmware was contained in EPROMs and initially comprised a 1kB 'monitor' providing control, and a 1kB tiny BASIC interpreter. Later, a more sophisticated 2kB monitor and 8kB BASIC interpreter was introduced to sit on an expansion board (so-called Level 7.2 software). There was also an elusive 8kB Triton Resident Assembly Language Package (TRAP). Until recently this was thought to be lost, but a ROM dump has turned up which is included on my GitHub site. Ultimately one could expand to a 24kB PASCAL compiler, or run the CP/M operating system (I did not get this far personally).

Input was through a standard QWERTY keyboard, supplemented by some hardware interrupt keys. Output was to a standard black and white analogue TV using a dedicated hardware VDU controller chip (the Thompson SFC 96364). Storage was provided by tape cassette with an interface driven by a UART chip.

Hacks

A Triton provided an LED output array which could be hijacked to drive other electronics, for example a teleprinter using a 5-bit ITA2 Baudot-type code. Conversion from ASCII and serialisation was done in software (8080 machine code). The baud rate was set by a timing loop with an elegant hack: an outer loop set the number of cycles in the timing loop and attempted to print a message including this number to the teleprinter. In the vicinity of the correct baud rate, this message would appear without errors and the correct value for the timing loop could be read off, like this :

...

TIMING LOOP DELAY = 07A5

TIMING LOOP DELAY = 07A6

TIMING LOOP DELAY = 07A7

...

A much more ambitious hack was to build a high-resolution graphics unit which intercepted the pixel stream between the output of the VDU controller chip and the UHF modulator. The graphics unit delivered addressable pixels at a resolution 256 x 192 — the image below shows the output from a recursive algorithm used to generate a fractal landscape drawn from triangles.

The tape cassette method of storage was so frustrating and unreliable that I later (circa 1995) hacked it to drive an RS-232 interface, first to a BBC micro, and later to a modern laptop, using a TTL-RS232 transceiver kit from MAPLIN based on the MAX232. This intercepted the 5V output of the UART before the tape cassette signal modulation stage. On the laptop side two bespoke C codes dealt with the data stream – these codes and associated material are now hosted in the above-mentioned GitHub repository.

More information is available including many of the technical manuals – copies of the manuals can also be found in Robin Stuart's GitHub repository. My own machine still exists but probably no longer functions as the IC pins oxidise and bit rot affects the 40-year-old EPROMs. Around about 1995 I took memory dumps of the level 7.2 monitor (2 x 1k blocks) and the 8k BASIC interpreter. These are available in raw binary and disassembled (flat ASCII text):

• V7.2 monitor 0x0000-0x03FF : binary and disassembled

• V7.2 monitor 0x0C00-0x0FFF : binary and disassembled

• V7.2 BASIC 0xE000-0xFFFF : binary and disassembled

These ROM dumps are also available in the GitHub repository along with instructions how to use them with Robin Stuart's SFML emulator; and I also provide sample machine code including a Galaxian clone!