Normally the root type is 628512 or 624000, the first is more common. It's a 32-pin DIL or SO outline, less common is the PLCC and TSOP variant. The organization is 8 bits wide, 512k, hence 4 Mbit.Dave wrote:I'm looking for quantities of:
512k SRAMs. What is their part number and organization?
There is also a 16x256k variant in a SOJ42 package and also a TSOP package, but it's less common and usually higher price. Fast 32x128k versions exist in QFP100 packages.
The 628512 (sometimes also labelled 618512) were commonly used as cache/buffers on old IDE hard drives, the 1-4G sized variety, also lots of embedded telecoms equipment. 16-bit and 32-bit wide versions were used for external cache memory on old Pentium 1 motherboards
27512 has a Flash variant made by a rather obscure manufacturer but it's not in-circuit programmable. Better use one of the smaller uniform sectored 5V flash chips such as the AMD/Spansion 29F010, 29F020, 29F040 series. These do come in 32-pin DIL cases but more commonly in 32-pin PLCC. For use as replacements for smaller size EPROM, tie extra address lines to fixed 1 or 0 depending on programming requirements. These can be in-circuit programmable and in fact it's possible to do it with a program written in superbasic assuming you can get a write enable signal to them. There is however the matter of sector size. Flash memory is divided into sectors that can be erased individually, so that partially reprogramming a chip does not require erasing the entire contents and then re-programming it. Each of the above has 16 sectors, 16k, 32k and 64k in size respectably, and they are 128k byte, 256k byte and 512k byte Flash memory chips. For storing something like ROM images, the obvious choice would be the 16k sector 29F010 as ROM images are a multiple of 16k - assuming the chip is large enough. Just like EPROMs, flash erases to FFh in all locations, except it does it far quicker and also either the entire chip or any selected sector. Writing is done similar to EPROM programming, you can only reset a 1 to a zero, but getting it back to one requires erasure. Unlike an EPROM, the chip actually contains internal hardware that does this. The software activates programming mode by writing a specific unlock sequence and then issuing appropriate commands and reading responses from the chip - the protocol is described in detail in the datasheet. The unlock sequence is designed to prevent accidental overwriting of the data, though for total protection once the chip has been written, pull the write enable line to 1 (perhaps a jumper can be used). The neat thing is that the protocol is the same for all chips in this series.27512 EPROMs, 27256 EPROMs, or their SMD flash equivalents (5v tolerant).
It is also possible to make a PLCC to DIL adapter board that can take these so they can be plugged into a 28 or 32 pin EPROM socket. Still the most cost effective choice is the 29F040 and is the last one that fits a PLCC 32 case, larger Flash memory uses TSOP or BGA.