80-Bus News

GM803

80-BUS EPROM/​ROM board from Gemini taking up to 16 EPROMs, either 2708 (1Kx8) or 2716 (2Kx8) types. Also has socket for Nascom 8K BASIC ROM. Incorporates ‘page-mode’ but not ‘Extended Addressing mode’. Was also available as a kit. Discontinued, to be superceeded by GM853.

GM804

A linear power supply for powering up to two 5.25″ floppy disk drives. Used inside GM805, GM815 and GM825. Only ever sold as a kit. Discontinued (although still used by Gemini in the GM825).

GM805

A single/​twin 5.25″ disk drive unit incorporating Henelec single density disk controller board and GM804 PSU. Pertec FD250 double sided 48tpi drives used giving 160K bytes formatted per drive. For use with Nascoms, connected to the system via the Nascom’s Z80 PIO. Discontinued.

GM806

A combined 5A power supply board, buffer board with ‘Reset jump’ circuitry, and 5 slot backplane for expanding Nascom 1 computers. Sold as kit only. Also sold in ‘A’ version without PSU components. Only ‘A’ version now available.

GM807

A 3A linear power supply unit suitable for powering small systems. Was also available as a kit. Now discontinued and replaced by various switch-mode units (see on).

GM808

An EPROM programmer for 2708 and 2716 EPROMs. Originally produced by Bits and PCs and later taken over by Gemini. Attaches to the system via a Z80 PIO. Supplied with software for use with Nascom and Nas-Sys. CP/M software for Gemini systems available on request. Only available as a kit.

GM809

80-BUS single/​double density floppy disk drive controller board. Supplied suitable for 5.25″ use only, but small modification possible to support 8″ only. Superceeded by GM829.

GM810

80-BUS motherboard incorporating 8 80-BUS positions (and connectors) and 5A linear power supply. Discontinued.

GM811

80-BUS CPU board. 4MHz Z80A processor, Z80A PIO, 8250 UART providing programmable baud rates, stop bits, parity, etc., RS232 interface, 1200 baud CUTS cassette interface, 8-bit input port. Most powerful feature of this board is the four ‘byte-wide’ 28 pin sockets that may be populated with EPROMs, ROMs or static RAMs from 2Kx8 to 16Kx8 (32Kx8?) per socket, thus making the board suitable for many control applications with, for example, 48K of EPROM and 8K of RAM on board. On-board memory may be switched out of memory map under software control. Memory decoding is provided by PROM which must be replaced if the standard 4 by 4Kx8 decoding is unsuitable. Normally supplied with RP/M monitor that emulates CP/M in a cassette based environment, and can also ‘boot’ GM809/​GM829 based floppy disk system.