INMC 80 News


May–September 1981, Issue 4

Page 57 of 71

128 characters in EPROM, and 128 in RAM. Single commands to the IVC card can define the 128 RAM characters as the inverse of the main set or as block graphics characters, giving a resolution of 160 x 75 blocks. Furthermore, byte patterns may be sent to the card to define your own characters.

The IVC card supports a wide variety of commands (sent as control codes or ESCAPE sequences.) These include insert/​delete character, insert/​delete line, clear to end of line/​screen, lock a portion of the screen from scrolling, invert/​blank the screen, set, test or reset a block graphics cell, return a line from the screen (yes, there is two way communication!), plus lots more.

Software to drive the card from the host computer is very simple. For owners of the Gemini G805 disk system, Richard Beal has already written a new version of SYS that supports this card (and also supports screen editing within CP/M!!)}. Nascom owners only need enter a short ‘U’ routine – however it must be pointed out that any program that is expecting the screen to be 48 x 16 and memory mapped at 0800-0BFF will not automatically adjust itself to the new screens’ format and position!

Disk card

Although the Henelec controller card used in the Gemini G805 disk system is very good, it does have several limitations – it is only single density, only supports up to 3 drives, and runs via the PIO.

The Gemini G809 FDC card is an 8″ x 8″ bus card. It supports Pertec FD250 (5.25″,​48TPI,​DS), Micropolis 1015 (5.25″,​96TPI,​DS) and Pertec FD514 (8″) disk drives and can control up to four drives of the same type. Up to 8 drives (2 boards) can be used in the same system. Density is either single or double, selected under software control.

CP/M 2.2 will be available to support up to 4 Pertec FD 250 drives with the Nascom. Using double density and 512 byte sectors this gives 350K per drive (formatted)! The software also supports SD Systems format to allow transfer of data to/from the Gemini G805 disk system.

The Other Card

With all of the above cards, Gemini have the complete range for a very powerful and flexible system, bar a minor item – a CPU card! Hence we have produced an 8″ x 8″ card which is just that. Although not of immediate interest to Nascom owners, this brief description completes the details of our product range.

The Gemini G811 CPU card utilises (yes, you’ve guessed it) the Z80A processor at 4MHz. There are optional wait states, and reset jump to any 4K boundary. Serial I/O is via a WD8250 UART. This gives programmable band rates, stop bits etc. Input/​Output to the UART can be switched between the RS232 and cassette interfaces under software control. The RS232 interface supports modem control and handshake signals; the cassette interface is 1200 band CUTS. A Z80A PIO is provided for parallel I/O.

Provided on the board are four ‘bytewyde’ 28 pin sockets – these sockets will accept a wide variety of RAMs/​EPROMs/​ROMs from the 1K x 8 static RAMs up to the latest 32K x 8 ROMs. (32K x 8? Yes!) The on-board memory block can be switched out of the memory map under software control, allowing a 64K RAM system to be fully realised.

The monitor is something special! Living at the top of memory (F000), to programs it pretends it is CP/M, plus it has a range of useful commands. You don’t have to have disks, but if you decide to upgrade to them later you can take all your software with you – and the monitor already contains the necessary bootstrap routines to run the Gemini G809 FDC card. This is real expansion without redundancy!


All of the items in the first part of this article are real products and available now. The last three items are finding their way into production as I write (they’ll only be available built and tested) and may well be on demonstration (or even available) at your distributor by the time you read this.

Gemini Microcomputers does no direct selling, and the above items are ONLY available (in the UK) from the following companies: Bits & P.C’s., Business & Leisure Microcomputers, Electrovalue, Henry’s Radio, Interface Components, Target Electronics.

Page 57 of 71