On Fri, Jun 5, 2020 at 10:08 AM, David C. Partridge wrote:
Looking at the datasheets these devices appear the be the same, am I missing
something, or was it just a case of the MCM68766 superseding the MCM68764?
AFAIR the two are mostly the same. The main/only difference is in the Enable lines. The 68764 has a Chip Enable(low) ('CE) line, which in the 68766 is an Output Enable(low) ('OE) line.
Data availability in the 68766 after 'OE is faster (100 ns) than in the 68764 after 'CE (450ns). OTOH, the ('CE) in the 68764, when high (i.e. Disabled), puts the chip in a low-power mode.
Raw read access time for both chips is the same (450ns) and 'CE is as fast as the delay from Address Valid to Data Valid with 'CE asserted. (Nominal max. times for the most popular versions).
If the low power capability of the 68764 is irrelevant, a 68766 will always do, the 68764 may not. I haven't checked if the 68764 will fulfill the 7854's timing requirements.
Raymond
Raymond Domp Frank