I have to order some new chips so I can burn a new ROM for my Ms. Pac / Galaga Anniversary PCB. The U14 ROM on the board appears to be bad. When I pull the sticker up it says "AT27C256R 12PC 9802". When I search Digikey they have AT27C256R-45PU-ND and AT27C256R-70PU-ND. The only difference between those two chips appears to be the access time. The first is 45ns and the second is 70ns. When I search for the proper number match though it comes up as obsolete and is no longer available. The only difference that I can see in the specs is the access time is 120ns.
My question is this, does it matter which one I order? Are they all compatible? Since my current chip is 120ns access time will it even matter if the new replacement has a faster access time? I can see a problem if the access time was slower but that's not the case. Any help or advice would be much appreciated. Thanks.
Robert
My question is this, does it matter which one I order? Are they all compatible? Since my current chip is 120ns access time will it even matter if the new replacement has a faster access time? I can see a problem if the access time was slower but that's not the case. Any help or advice would be much appreciated. Thanks.
Robert

