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
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
Optionally, the WD2793
can be fitted instead and a few
links changed to make the
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
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
page size is 32K. With the
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
& 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
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.
256K Dynamic RAM card is limited to a single card with the
CPU card (and
probably Nascom-2 too), although up to 2Mbyte (8 cards) can be added to a
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
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.