INMC 80 News


May–September 1981, Issue 4

Page 56 of 71


Our attention now turned to the Nascom 1. Expansion of this had always been a messy business as, when Nascom 1 was originally designed, it wasn’t really expected that anyone would wish to add anything! All owners of expanded Nascom is will no doubt painfully remember soldering 43 way ribbon cables, and the dreaded memory plague.

The Gemini G806 Supermum is a 12" x 8" board that sits back to back to the Nascom 1. It provides a 5A PSU, 5 slot motherboard, and a buffer section. The buffer section provides reset jump facilities and gates Reset with M1 – something the Nascom buffer board should have done but didn’t. Connection between the Nascom 1 and Supermum is via a mini 43-way motherboard.

64K RAM Board

With the advent of disk systems peoples greed (and need) for more and more memory was rapidly growing. The obvious solution – a single board giving a full 64K of RAM.

The Gemini G802 ‘RAM64’ is a RAM board kit, available in 16, 32, 48 or 64K sizes. The bus ‘RAMDIS’ signal, giving priority to EPROM/ROM in the system, means that a ‘RAM64’ board of any size can be used without any data clashes. Additionally a page mode option is available (see EPROM/ROM board) allowing four cards to be added to the system. Although the Page Mode System is relatively unexplored as yet, there is a lot of potential for, for example, phantom disk drives with instant access!

‘RAM64’ is a full 4MHz board with flexible address selection to 4K boundaries. The board is also available built and tested fully populated (64K) and complete with page mode, at a very silly price. (Cheaper than some of the kits!)


Other existing Gemini products are the Gemini G807 3 amp power supply, Gemini G601 Reset jump kit (fitted to the Nascom buffer board to give ‘reset jump’ to any 4K boundary) and Gemini G808 EPROM programmer. This latter item, produced in conjunction with Bits & P.C.’s., connects to the Nascom PIO and can program multi-rail 2708 EPROMs or single rail 2716 EPROMs. Two low insertion force sockets are provided for ‘Donor’ and ‘Recipient’ EPROMS. Software is supplied on tape (N2 format) and can program from the “Donor” or RAM, and read and verify EPROMs.


About to be launched by Gemini are three new 8" x 8" boards, two of which can be used with Nascoms.

Video Card

There has long been a requirement for an 80 x 25 video card for professional applications and for use with disk systems with CP/M, where many software packages expect a screen width of at least 72 characters. The trouble with a screen of this size is that it requires a 2K block of memory to be located somewhere and, if the screen routines are going to support a wide variety of functions, getting on for another 2K of memory to hold the software. The solution then, with this card, was to make it I/O mapped and intelligent!

The Gemini G812 Intelligent Video Controller (IVC) card is Z80A microprocessor controlled. Two screen formats are supported by the card – 80 x 25 crystal controlled, plus an adjustable dot clock to give a second format (set to 48 x 25 as supplied.) Output from the card is a 1V peak to peak composite video signal for driving a monitor – with 80 character wide displays, TV sets are not recommended.

The IVC occupies three I/O ports of the host system. Port Bl is for bidirectional data transfer, B2 provides handshake signals, and port B3 is used to reset the card independantly of the system reset. The character set on the card gives

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Page 56 of 71