Quote:
Originally Posted by ajgriff
Quote:
Originally Posted by ajgriff
One thing worth noting is that Colin's PET is fitted with sixteen TI 4108 dynamic RAM chips (see post #8) whereas the circuit diagram we've been working from has sixteen 4116 chips ie, as in the PET 3032. This is significant because I can't find anywhere currently selling legacy 4108 chips. On the other hand NOS 4116s are still available, possibly because some versions of the Spectrum used them. In fact there's one vendor offering eight 4116s for £10 plus £1.60 p&p. In theory and with changes to jumper settings it would appear that eight 4116s could be used as direct replacements for the sixteen 4108s in Colin's machine.
|
If the buffers check out and with Colin's ability to socket multi-pin ICs it's well worth considering these:
https://www.ebay.co.uk/itm/STC-4116-D-memory-ic-ram-QTY-8/393015482007?hash=item5b818c5697:g7kAAOSwMFhfrqUA
The only problem is I can't find a datasheet for these STC chips but the seller seems to have dozens of them so upgrading to 32k could even be an option.
Alan |
STC 4116 are just standard generic 4116 (which are 3 supply, whereas the 4816 used in BBC's are 5V only)
https://www.petervis.com/Sinclair/Si...tatic_RAM.html
- The ZX Spectrum had many of these ones (2N = 200ns?) originally fitted.
Although it's not clear what speed 4D marked ones are. It doesn't seem that DRAM were ever 400ns, and that a higher single number on some were actually faster (and same coding may be used by other manufacturers):
https://www.electronicspoint.com/for...m-parts.65261/
TMS4532 and OKI M3732 were the one-half reject faulty 4164's (= M3764's) (single rail) DRAM's
DRAM IC's are inherently a 'square array', due to Row/Column addressing.
So standard all-working sizes will be 1, 4, 16, 64, 256 etc.
Most were 1bit only, so needed 8off.
But later on 4bit ones (usually with 1 changed to 4 / an extra 4 inserted into part no.) were released, to minimise chip-count. And revised versions of many computers (and PC memory modules) used these.