Scor­pio News

Documentation

This is adequate and consists of a detailed explanation of the port allocations and their functions, program examples for the insertion of support for the VFC into a CP/M BIOS or interfacing the VFC with NAS-SYS, and details of the control codes which the VFC recognizes. In view of the large number of possible combinations of VFC and Nascom 2/​Gemini/​MAP CPU or FDC cards, the implementation notes are quite extensive. They are also easy to follow which makes a pleasant change from some systems; unfortunately, no details are included for the Nascom 1 and I gather that there are difficulties in using the VFC with it. In the full version, 15 or so links are involved but not all of these have to be used. Details are also given of modifications which need to be carried out if RAM boards (Gemini and Nascom) are to be used. No modifications are needed if the MAP RAM card is used. A final section gives details of pin assignments on the VFC and a useful note on TEAC, Pertec end Micropolis drive pin assignments.

If the fully implemented VFC or the FDC-only system is purchased, MAP-80 Systems can supply s fully licensed version of CP/M 2.2 or 3.0 with a customised BIOS. This is supplied with a short instruction manual which explains how linkages are made or modified on the various types of CPU cards, gives details of disk error messages as well as how to customise the BIOS for other features. Both parallel and serial printer output and screen editing using ^@ are supported A special boot PROM is supplied which replaces the RP/M boot EPROM if the CPU card it a GM813.

In addition to the usual CP/M files on the disk, and the customised MOVCPM.COM or CPM3.SYS, a multi-utility program is supplied, which allows users to format, verify or copy disks. MAP will also customise existing users’ CP/M on request at a reasonable cost.

THE VFC IN USE

The fully implemented card has two 3 pin connectors for the video input and output, which are incompatible with the Gemini GM812 IVC video output which is a standard jack socket requiring an enormous plug. Why Gemini use this gargantuan means of taking out the video puzzles me since Nascom found some small coaxial connectors for their AVC which are really neat. I’m not all that keen on MAP-80’s connector either and I’m sure that there must be all sorts of impedance mismatches since neither type is likely to approach 75 ohms or whatever a monitor is supposed to need to produce a good display. The keyboard and disk drives are plugged in to the board – using non-latched ID connectors which are a little difficult to unplug when needed.

On booting up, a systen message is displayed together with the CP/M prompt; commands may then be entered. The display is 80 columns wide and because of the alternative character set, both normal or reverse (black on white) characters can be displayed, or an alternative character set which can be programmed into a 2716 or 2732 EPROM and plugged into the second ROM socket.

The memory-mapped display appears to be quite fast and free from visible interference as a consequence of CPU and CRT controller interaction; as has already been mentioned, the Gemini video controllers have Z80 CPUs on board and under certain circumstances on the IVC some interference can take place which produces a faint diagonal patterning on the screen – which can be irritating under some screen display conditions. The cause possibly lies in the layout of the IVC board where one or two long-ish tracks radiated noise which was picked up by other parts of the system. This problem appears to have been resolved with the Gemini SVC which has a much more legible screen display than its predecessor.

I experienced no problems with the floppy disk controller when using Pertec (48 TPI) and TEAC, Canon or Mitsubishi (96 TPI) drives – which are plug-compatible. The Mitsubishi drives were quietest in operation. Some problems were experienced when using 96 TPI Micropolis drives – I’m not sure why – perhaps they objected to the fast track stepping rate which suits the TEAC and