April/May 1980, Issue 7

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MORE RAM and a B-BUG note


by G. Alabaster

Minimum Nascom 1 with Nasbug T2 ? Then you NEED more memory and have an empty EPROM socket.

Well, there is a nice static RAM chip, the MK4118, which is pin compatible with the 2708 EPROM. I should say ALMOST pin compatible. This is a way to put the chip in, leaving the board and socket unadulterated in case you wish to put an EPROM back there.

Here are the pin out differences:

Pin No.   2708         4118
18        Program      CS
19        VDD (+12V)   L (RD)
20        CS           OE (RD)
21        VBB (-5V)    WE (WR)

The pins on the MK4118 would object to being bent out, so put a socket with flexible pins between the RAM and board socket (See Dr. Dark’s Page – Ed.). Bend out pins 18, 19, 20, 21. Connect leads to these pins and connect to the printed circuit as required. The points I used were these:

Pin 18 to E select line which has a through plated hole near pins 12 and 13 of IC36.

Pins 19 and 20 connected together to the inverted Read Data line which has a through plated hole just out from pin 9 of IC44.

Pin 21 to the inverted Write Data line which has a through plated hole near IC50 going to pin 3 of IC50.

As an extra safety measure, put insulating tape over the board socket holes for pins 18 to 21 and double check the voltages at the intermediate socket without the RAM in.

At the time of writing there is a worldwide shortage of MK4118s, but this should ease off once the backlog of NM’s order for Nascom 2 requirements has been met. Ring around the suppliers, you could be lucky as you only need one. With time the price should drop quite a lot from the present twenty pound level.


Mr. F. Whitby wrote in to inform us that when using the 8K BASIC (or any other program), you get “Escape” by holding down “@”, then pressing “Shift” and holding it down, then pressing “3”.

All other control keys are different with B-BUG, as the B-BUG manual explains.

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

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