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
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.
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