g812
The EPROM with the damaged label, to the left, is IVC-MON 1.0
This was a very clever card at the time. The IVC (Intelligent Video
Controller) had only a mono display, but the resolution was variable. It
made an excellent display card as it could emulate the standard Nascom
display and also display graphics. The cost was also reasonable (as
these things went at the time!) so it proved to be very popular. It was well named, as it included its own Z80A processor, 2kB RAM, CRTC chip and operating system in EPROM. This made it independent of the main Z80. Only 1kB of the RAM was actually used, the remainder could run user programs.
Being designed to be Nasbus-compatible, it would work with either existing Nascom or the new Gemini systems that were just starting to appear (with the new G811 card).

An unusual addition was a parallel keyboard input for use with Gemini keyboards. (Gemini GM821 Cherry 59-key or GM827 Rotec 87-key). It was thus possible to build quite a nice system using just this card with a G811 CPU/Bytewide ROM/RAM card or G813 CPU/64k RAM card!

  • Dedicated Z80A processor
  • 6845 graphics control processor
  • 80 characters 25 line mono main display
  • Second width-programmable mono display (supplied as 48×25)
  • Inverse display possible
  • 128 Programmable character generator
  • 128 Fixed characters in ROM
  • 160×75 “pixel” graphics
  • Keyboard input (Gemini keyboards only)
  • Combined video output (not via an RF modulator)

This card was designed to run without using the main computer’s memory. A system of commands was sent to the board via three I/O ports. Because of this, existing software using the NASCOM memory-mapped display would not work. Another problem with this form of communication was that of rather slow scrolling of the display, since that was generally handled by the main CPU card.

An unusual choice of connector was used for the video output. If you
look at the top of the card in the picture you can see a standard 1/4 inch “jack” plug – not normally associated with video signals!

GM812 IVC Hardware Manual

GM812 IVC Software Manual

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