INMC News

  

April/May 1980, Issue 7











Page 23 of 39











Nascom 2

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 is suspect.

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 of IC31.

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 of IC31.

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.


This is an OCR’d version of the scanned page and likely contains recognition errors.











Page 23 of 39