Scor­pio News

  

April–June 1987 – Volume 1. Issue 2.











Page 45 of 51











The MPI is supplied either ready built, or as a kit. A number of options are available:

FDC and Winchester controller
          (2797 or 2793 FDC Controller, depending upon system)
CTC
SIO

The board or kit is supplied with the appropriate combination of options as ordered. The PCB is the standard 8″ square, with the usual Map 80 blue resist and high quality. Kit assembly is quire straightforward and the instructions are reasonably clear – there is a separate assembly manual which I didn’t receive but a phone call to Map soon solved the problem.

There are 22 Links on the board, some of which are not needed for standard configurations and a 20 way link header to be wired up if one wants the SIO and/or CTC facilities. Details of the link functions and also the changes necessary to accommodate the 2793 controller, if the board is to be used as a Lucas/​Nascom compatible FDC, are provided.

A slight disadvantage is that the instructions are not very clear on which links are needed for particular uses – my boards have Links 2 (a-b),3 3 (a-b),6 (a-m). 13 (a-m), 14 (a- 13n) 15 (a-c), 16 (COM-E), 17 (b-c),​18 (c-6, d-5), and 21 (a-Clk). Map will supply details of modifications required to read odd disk formats with bad side 2 flags, which might be necessary if you wish to use their Format transfer program. No details are provided of the crystal frequencies or types required for on-board frequency generation.

The SIO and CTC seem to be standard implementations using the Z80A CTC and SIO chips. The circuitry around the 2797 seems to be almost identical to that used on the VFC and the RS485 interface is provided by differential line driver and receiver (75174/​75175), in contrast to the R5232 interface which uses the conventional 75188 and 75189 types.

My main use for the MPI is as a Floppy/​Winchester controller and both the ready-built and kit versions have performed without trouble with a wide range of other boards from Nascom, Map and Gemini. In particular, the combination of the MPI with TEAC compatible drives and the Map version of CP/M Plus provides fast, quiet disk access – I hate noisy computers!

As I sometimes need to copy disks with peculiar formats, the small modifications to the board for this purpose are easily made. I don’t need to use either the SIO or CTC functions (although they are implemented on one of the boards) – I use the Serial o/p on the Map or Gemini CPU board for this.

The fully-assembled version with FDC, CTC and SIO options is possibly a bit pricey at £195 + VAT but money can be raved by building the kit yourself – not a long job – possibly a couple of evenings. Host users need only the FDC/SASI version and this is quite a bit cheaper. I haven’t seen an up-to-date price list from Gemini or Map but suspect that the ready built FDC/SASI is about the same price as the GM829 or GM849 (£145, in the last price list I saw from Gemini). It would be worth contacting Map to see what their current prices are like.

I can thoroughly recommend this product for anyone contemplating upgrading an 80-BUS system even if they already have the Gemini 809 FDC, since it will enable them to take full advantage of higher access speeds and quieter operation if the newer TEAC-compatible drives are used. [Ed. – alternatively readers may like to make the the GM809 modifications shown elsewhere in this issue.]












Page 45 of 51