The VFC video/floppy controller was quite a card. It allowed a floppy-based system to be built by adding a CPU/RAM card. It was available either ready built or as a kit, in which case you could build it with whatever options you required. It would work with the Nascom-2, GM811, GM813 and MAP-CPU cards. An on-board EPROM contained VSOFT, routines for controlling the hardware. There was no on-board CPU, so all operations were carried out by the main system processor. Hardware was mapped into a block of 16 Z80 IO ports, which were normally at E0-EF (but C0-CF could be supplied as an option).
VSOFT was supplied as part of the basic card. Any or all of the Video, Video Switch, Floppy or Keyboad options could be added to it.
Video
The display was 25 lines of 80 characters and was based around a 6845 video processor chip. Character handling was carried out by the main system CPU using routines in VSOFT. An EPROM socket was provided for a 2716/2732 EPROM containing an alternative character set. This could be switched in under software control. An optional video switch could be added, which could allow a pass-through from another video source such as the Nascom-2 video output under software control. Control codes were similar to the IVC but there was no facility to load & run programs on the card (as there was no CPU). Almost all the screen and character handling commands were identical, but there were differences in character set selection. There was no light pen support.
Keyboard
This was provided as a parallel input port with a strobed latch. It was read via VSOFT. The strobe polarity could be inverted to suit the keyboard.
Floppy Disk Controller
This used the WD2797 and was compatible with the GM809. 5.25″ or 8″ drives could be selected via a link (no software control).
MAP80_VFC_Software MAP80_VFC_Circuit Map-80_VFC
(Most info on this page from article by Michael Newson in Scorpio magazine)
nascom.info 