Scor­pio News

MAP-80 MPI – Multi Purpose Interface

This card is primarily a disk interface card, capable of talking to 3″, 5.25″ and 8″ floppy disk drives. A SASI bus interface also allows connection to winchester drives, via a hard disk controller card. As well as these, it provides communications via an onboard CTC and SIO with RS-232 and RS-485 (high speed multi-drop) interfaces. The board is addressed as 16 ports, starting at 00H, 20H, 40H … etc. (link selectable: E0H is recommended with VSOFT).

The floppy disk controller section uses the WD2797 as standard, configured to make it compatible with the GM809, GM829 and GM849. Optionally, the WD2793 can be fitted instead and a few links changed to make the MPI operate as the Lucas-Nascom FDC. SASI, 5.25″ and 8″ drive cables may all be attached simultaneously. The drive size (clock) is software selectable, and with suitable software switching the maximum stepping rate of 6mS for 5.25″ drives can be reduced to 3mS by selecting 8″ mode while stepping.

The CTC may be clocked either from the system clock or from two (user supplied) crystals. Output from the CTC can be link selected to clock the SIO for communications: 1 x RS232 input, 1 x RS-232 output, and 1 x RS-485 bi-directional high-speed multi-drop (2 x data, 2 clock lines).

MAP-80 256K RAM

While the Nascom-2 on-board RAM can be used in conjunction with another RAM card e.g. Gemini GM802, the system really takes off when more RAM is available for use as a virtual disk as it allows programs to run at RAM rather than disk-based speeds.

The 256K RAM card pages memory into the Z80 memory map, unlike the Gemini RAM-Disks, which are accessed on a port basis. When used as virtual disk there; doesn’ seem to be much to choose between them, BUT if you plan to run Map-80’s implementation of CP/M PLUS, then you will need the banking facility offered by the 256K RAM boards. This is because parts of the OS are held in different banks, and the TPA is actually in bank 1. Don’t bother with Non-banked CP/M Plus on a 64K system, it doesn’t have the full range of facilities – use CP/M 2.2 instead. Both 2.2 and Plus are available, configured, from Map-80. If you already have CP/M, they will customise yours to suit.)

The size of page paged depends upon the processor card used. With the Nascom-2 and GM811 the page size is 32K. With the GM813, any 4K block can be mapped into any 4K slot in the Z80 memory map (A19 may need to be connected to the bus – see “The Great A19 Debate” 80-BUS News Vol2 Iss.1 p43). Selections of the mode and card addressing is performed via two link blocks. When these cards are supplying all the memory in a system, there is a facility to force Page 0 into place (link and software selectable) so that there is a common area of memory in place for program execution. The maximum paged RAM supported as standard is 1Mbyte, but there is no reason why Gemini Ram-disks (GM833 & GM873, which are port accessed) should not exist in a system at the same time – if you’re rich enough. Even if you only have a GM802 64K RAM card, modification details are given to use it in conjunction with the Map 256K RAM. The minimum memory which can be fitted to the card is 64K, and further 3 banks can be fitted as funds permit to make up the full 256K.

The GM862 256K Dynamic RAM card is limited to a single card with the GM811 CPU card (and probably Nascom-2 too), although up to 2Mbyte (8 cards) can be added to a GM813 based system. Its mapping arrangements are different to those employed by the Map 256K RAM, paging 56K, 60K or 64K pages with 8K, 4K or 0K of common memory when m page mode; or usable in 4K mappable blocks when used with the GM813.

All in all, a very powerful and flexible system can be assembled as described above, but never lose sight of what you aim to achieve with your system. It can only ever be as good as its software, and you must either ensure that software support is available for the products you wish to incorporate, or be prepared to do it yourself. (Map-80 are able to supply modifications for SIMON and RP/M to allow them to work with their various products.)

On that point, I close by stating that although I have no links with Map-90 (other than Adam!), they have always been most helpful with any questions or problems. The provision of circuits and sources is also most welcome as it is always better to have them and never need them than the reverse. I do not mean to slight Gemini is any way for their products are first-rate, it’s just that while I developed my system over the years, I made my choices with an eye to future flexibility based on what was available as well as cost.