Nascom News­let­ter

On Heat.

Rewarming a cold start is not for the faint-hearted, maybe my hardware problems are confusing it all, but I have not succeeded (is my meory RAMshackled?). In fact, I have several times killed text (with and without extension) totally but refound that text in Nas-Sys by filling suspect locations with 20H, removing the stop FFH character at 1021H and then putting the correct end-of-file address in 101BH and 101AH (high byte in high address). The location 101CH can be ignored it seems, Tabbing upwards from 1021H (in 0EH blocks) it is obvious when the end-of-file appears. You will see about 8 FFHs or at least the end of your schpiel. Take it from me, you can reheat Naspen too often.

RAMbling on

What is the best way to psych a chip? I find that the hottest ones are generally candidates for replacement when searching for faults. Using one of the more sensitive parts of the body as a thermometer gives rise to in-jokes about kissing RAMs, not to mention BUS drivers. Jest not, it works. Experimentors are advised to switch off first – 4MHz tastes vile!

PROMulgating

I don’t recall seeing any review of the I/O PROM programmer but having used one for six months, I am full of praise. In fact, the only real hassle was having to solder one cable end and the PROM personality plug. The software is the operating manual almost, which is how programs should be – at man’s service. It covers 2708, 2716 and 2732 PROMs but with a little guile 2764s and 27128s can be accomodated. Points to note are the need for 21 volts not 25. If you need the faster 2732A, beware of the same lower programming voltage requirement.

Chipping in

CMOS versions of everything are pouring out from all manufacturers. National have a Z80. They, Motorola and RCA have many 74HC series parts fast enough and beefy enough to do most TTL tasks. Projects planned for your intrepid reporter include using CMOS 2716s, first to reduce power to 10mW per PROM and also to keep things cooler. After that, the hottest parts are the Z80 and bipolar PROMs. Another project is to try using X2816s, they are 5 volt only EEPROMs made by Xicor. If you have £28 plus VAT (Vear and Tear), professional users can get them from Micro Call, Thame, Oxon (tame oxen indeed). The nice touch is that they sport on-board latches which means that providing you only write to them once in 10mS they behave like 2K, non-volatile RAMs. I have experimented with them but the first try failed. We are close though, so stay tuned to this channel folks. Unless anyone has tried using 2816 or 27c16s, in which case they can write to Cresby (in a plain, brown envelope).