The Tangerine Microtan 65 was first sold in 1979. The philosophy of the Microtan
65 was expandability. The basic system sold as a kit for £59.95 +
£1.50p&p and was a 6502 running at 0.75MHz, 1k RAM, 1k PROM, a TV interface (16 lines of 32 characters) and a keyboard interface. The system monitor, TANBUG, was held in the 1k PROM and provided commands to view and modify memory and run and debug programs. Later revisions held TANBUG on a 2k EPROM. Similarly priced systems which were available at the time (the Acorn System 1 and the Sinclair Mk14) used 7-segment "calculator" displays instead of TV output and were not as expandable.
This basic system could be expanded to suit your needs and funds:
- The keyboard could be either a 20 key "hex" keypad or a full ASCII keyboard.
- Lower case characters.
- "Chunky" (64x64) graphics.
- A case!
To expand further, you needed a backplane. Two were available:
- Two slots - for the CPU board and the Tanex expansion board.
- Eleven slots - one for the CPU, one for Tanex, one for TanDOS and eight general purpose.
The first expansion board was Tanex:
- Upto 7k of RAM
- 6 EPROM sockets
- 2 6522 VIA's
- A serial interface with RS232, TTL and 20mA current loop.
- A tape interface
It was possible to buy a Microtan 65 CPU, small expansion backplane and an
expanded Tanex as a complete system. This was known as a Micron.
EPROMs that were available from Tangerine were:
- XBug - a monitor extension providing tape save/load, assembler and disassembler
- Microsoft BASIC
There were also many third party EPROMs: word processors, games, BASIC extensions...
One other variation on the system appeared in Electronics Today International magazine in 1980. This was a Space Invaders machine designed around the basic Microtan board, with additional hardware to generate the sounds. ETI's sister magazine, Computing Today, also had an article giving the game listing (which could be loaded into the RAM on the Tanex board) and the sound hardware (which could be plugged into the keyboard socket). The listing appeared as a raw hex dump covering nearly two sides of A4. Back then, it took me two days to type it in and debug it (it was easy to confuse "8" with "B" and "0" with "D"). After writing the emulator, I scanned the original pages, tidied them up and OCR'd them. I got the whole thing working in under 2 hours!
Tangerine sold the rights to the Microtan to Microtanic Computer Systems, in order to concentrate on their Oric system. Microtanic continued to develop additional cards for the system for a number of years. In the end, there were many boards available to fit the eight general purpose slots developed by Tangerine, Microtanic and other third parties:
- High resolution graphics (256x256, B&W, but you could sync. three together to give RGB output).
- Sound (one or two AY8912 sound chips)
- Banked EPROMs
- Floppy disks
- Additional and alternative CPUs (the 6809 was popular, and had FLEX as its DOS)
- Real time clock
- Colour 64x25 teletext type display interface
- EPROM programmer (this appeared in ETI magazine)