g811
This was Gemini’s first processor card, later replaced by the GM813. It was intended to replace a NASCOM-1 or NASCOM-2 as the CPU on a NAS-BUS system and to be the main CPU on the 80-BUS. With the advances in technology since the NASCOM-1 days, Gemini had, effectively, put the CPU and ROM systems together on the same PCB. This board did not have the expansion capability of a NASCOM-2, though it included a Z80 SIO, a 8250 UART and a cassette interface. This PCB could use either serial or parallel ASCII keyboards. Alternatively it could recognise a keyboard connected to a video card. The processor was the tried and trusted Z80A running at 2 or 4MHz.
There were 4 “bytewide” sockets for RAM, EPROM or ROM chips. The monitor fitted as standard in one of these was an early version (often 0.1) of a 4k ROM called RP/M – Rom Program for Microcomputers (written by the writer of NAS-SYS). This looked, to programs, like a CP/M operating system. It was possible to write, run and debug small CP/M applications without having a disk drive installed! These could then be re-loaded from tape when disks became available. Indeed, Microsoft’s MBASIC for CP/M would run if loaded from tape or EPROM.
If the remaining 3 bytewide sockets were fitted with type 6116 RAM chips (the only bytewide RAM chips at any reasonable cost at the time), then there was 6kB RAM available on board, not terribly useful so a separate RAM card was almost always used.
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