GM886 Boot

GM886 Working2Yes, you see it right. Not a Z80 in sight, apart from on the GM832 SVC video card behind it. šŸ™‚

This board has an Intel 80286 with 1MB of RAM on board. I know of three still in existence, all set up the same and apparently working, but without any information on them.

Can anyone help please?

This is probably among the last of the Gemini cards to be released. There are higher numbers in the sequence, but I think those cards are ones where Gemini took over the sales. Imminent availability was announced in October 1987, at a price of Ā£525 plus VAT. That would probably make it almost Ā£1500 today (July 2020). It was quite expensive.

GM886 Top 1a

The 80286 CPU is the square chip above the empty socket at the left-hand side. The standard version ran at 8MHz, but there was an option available for 12MHz.

The 2C87 ceramic chip just above the processor  is a maths co-processor, taking some of the calculation load off the 80286. The empty socket below the CPU was probably intended for the alternative 80287 maths co-processor package. Also on board are a 8250 UART for serial communications (the same chip used in the IBM PC) and a 8255 PIO for parallel connections (including parallel printer interface). Close to the PIO is a HD14681 real-time clock. The 1MB of 16-bit RAM is provided by the eight 256Kx8 chips in the centre of the board. The two EPROMS make up 64K of available ROM space.

GM886 Top 2a

Apparently this board, like the IVC and SVC boards, could communicate with a Z80 CPU board on the system using I/O ports. This allowed dual processor operation.

The board would, apparently, run some MSDOS programs but with limitations on the display. It was stated that it could be used with the Pluto graphics card.

All photos provided by James and a bit mashed about by me to fit them in. šŸ™‚ Thanks James!


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