1) Try the board and see if it runs Basic reliably. If so go to step
3. Don’t bother to investigate further unless the board reliabilty
2) Grid the back of the pcb and change the resistors as for Nascom 1.
3) 1f you want the board to run at 4MHz without ‘WAIT states’:
a) Cut the clock line from the bus connector, 5, to pin 3
b) Connect a wire link from the clock side of the cut
track to pin 9 of IC35. Connect a 1K pullup between
pins 8 and 14 of IC35.
c) Connect a wire link from pin 8 of IC35 to pin 9 of
IC34. Connect a wire link from pin 8 of IC34 to pin 3
A number of boards have been fitted with the above, and all
have behaved perfectly. If you have a board which has been fitted with
the earlier Nascom 1 mods, and is working correctly, then: leave well
alone. If for some reason you wish to incorporate the above, then
remove any earlier mods first. All this brings us to another review.
NASCOM RAM B
Nascom RAM B is part of the new System 80 and is a RAM card
designed to replace the Nascom Series 1 Memory card. It incorporates a
number of novel features, and as far as we can tell has been fully
debugged. The RAM is organised as three blocks of 16K, using the now
popular 4116, 16K x 1 dynamic RAM. This gives the board a total
capacity of 48K, there being no onboard EPROM sockets, unlike Series 1.
The RAM is fully buffered in and out, and active delay lines are used
to get the timing ‘just so’. There should be no problems of the sort
experienced with Series 1.
The novel part is in the way the board is controlled. When
purchased, the RAM is just like any other RAM with a maximum capacity
of 48K (you can always buy the 16K version and fill the rest up later).
However, an option pack will be available which when added to the RAM
gives two important features:
1) Selectable ‘WRITE protect’ on each of the 16K blocks, controlled by
miniature switches mounted on the front of the pcb.
2) The ability to turn the RAM on and off under software control in one
of four ‘fields’ (or blocks, or whatever) by the use of a port. This
means that up to four cards could be co-resident at the same
address, and controlling software could select each as required.
This gives the Nascom system a total of 208K of addressable memory
(4 x 48K + the minimum system). Nascom claim this as a ‘first’ and
it certainly seems a very clever idea, although we wonder what you
could do with all that RAM if taken to extremes. Certainly faster
than disc, but what do you put in it ?
We haven’t played with a production version yet, but the
production prototype worked faultlessly (4MHz and no ‘WAITs’). We
understand the price will be about the same as the Series 1 RAM.