What Eprom Chips Do I need?

[jay]

  I've come up with blanks....

I thought he was looking for blanks 

[stayouttadabunker]

  I was speaking figuratativilty          (huh? I can't spell today...it's friday  )  .....arghhh! whatever....lol

[StatFreak]

SB, that was a good idea, but it turned out to be a bust. I called Mouser and they said that they don't have a cross-reference book (or computer program). He said that all they they could do would be to go by the data sheets just as I did.

Of course, those aren't much good if you don't know the correct replacement chip number!

It looks like I'll have to get the original UV chips for the 4MB applications.
I wonder why SST made all of the smaller SF chips backwards compatible but not this one? After all, we're talking about the swap of only two pins, not a completely different configuration. 

[Foster]

Using a low profile 32 pin socket and ZIF socket you could make an adapter to use SST 29f040? chips in place of the 27C040

Would also depend how much room you have above the original socket.

Optional install a very small DPDT switch on the adapter between those pins and you could have a switch in one position swap the pins for the flash chips and the other position be normal for your 27c040 chips.

[StatFreak]

Using a low profile 32 pin socket and ZIF socket you could make an adapter to use SST 29f040? chips in place of the 27C040

Would also depend how much room you have above the original socket.

Optional install a very small DPDT switch on the adapter between those pins and you could have a switch in one position swap the pins for the flash chips and the other position be normal for your 27c040 chips.

That could work. Would I use a piece of prototyping board to reroute the pins? (32 pin low profile socket plugs into the slot board, with the prototype board on top and the ZIP on top of that to the side? Or did you have a different approach?)

[Foster]

I was thinking just use small wire and solder to the 1 and 31 on ZIF
Insulate them with heat shrink

Carefully fold them under and run the wires to switch or the socket depending how you decide to do it
if you use the switch then from the ZIF to switch
connect the pins from the low profile to the common poles

then use 2 short wires to make an X between the ZIF pole and the remaining.
It is the same trick used in some toys and such to reverse the direction of DC motors

Let me see if character diagram will help
Double Pole Double Throw Switch (slide style)

1         2  one pin of ZIF pins 1 and 31 to each pole (1 to 1, 31 to 2)

3         4  one pin of low profile pins 1 and 31 to each pole (1 to 3, 31 to 4) Common poles

5         6 now make an X with 2 wires from these pins to 1 and 2 (1 to 6, 5 to 2)

One position of the switch it will be for the 27c040 and the other for the SST chip


Mount the switch to the ZIF so ZIF still functions then run the wires to the low profile and stack the 2 sockets. so that the other 30 pins make proper connections.
Wire wrap or such wire would be best. you want the sockets to be tight. test and secure everything together.

This is similar to stacking say 2 different PROMS in a game and changing between them by a switch. Except you solder the 2 PROMs to each other except the Chip Enable or such and run those to a switch that connects to the socket's Chip Enable.

[StatFreak]

Now I understand. Thanks Foster. K+