On Tue, Aug 30, 2016 at 1:28 PM, Paul Koning <paulkon...@comcast.net> wrote: > Another possibility would be a current (not surplus) DRAM device such as a 1M > x 16 chip, plus a couple of level shifters to go between the 3.3 V it likes > and the 5V logic of the Pro.
WARNING: Most recent 1Mx16 DRAM devices are synchronous DRAM (and usually DDR of some description), which are NOT EVEN CLOSE to being electrically compatible with legacy 16-pin DRAMs, nor even the 1 Mbit and 4 Mbit legacy DRAMs. Most of the ones that aren't synchronous are 3.3V parts, and won't work reliably if at all in a 5V system without the level shifters Paul mentioned. I commonly use 74LVC245 buffers between 5V and 3.3V logic, when the 5V logic doesn't require a full 5V swing (e.g., Voh min of 2.0V for TTL-compatible parts). It does appear that ISSI still makes some 5V 1Mx16 non-synchronous DRAMs in either EDO or Fast Page Mode. There's a reasonable chance that the 5V Fast Page Mode devices would work for replacing legacy DRAM, and wouldn't require any level shifting. Mouser has some in stock, e.g., the IS41C16105-50KLI in SOJ-42 package at $7.20 each (quantity one) or the IS41C16105-50TLI in TSOP-44 package at $7.02 each (quantity one).
