On Wed, 6 May 1998 20:02:01 -0700 Bob Newhart writes: >Does anyone know of a serial static RAM I could use for additional PIC >data memory? I am attempting to alter a pre-existing design that uses >93C66 EEPROMs, so something with the same pinout and bit-banging >scheme >would be nice, although not absolutely necessary. I don't care >whether >the SRAM is volatile or not. Look at the Ramtron FRAM's. These are intended to drop in in place of EEPROM (both Microwire and IIC models available), but write "instantly" like RAM and withstand more cycles (10^12 cycles IIRC). However, unlike EEPROM, read cycles will wear the device out just like write cycles do. Unless you're reading constantly, they should last long enough. The stored data is easier to glitch than EEPROM, but you don't care about that. Also they only work up to temperatures of 85C, period. > >The only firm requirements are three pin interface, minimum 64 bytes >RAM >per chip (bigger is better), and no write cycle limitations like those >associated with EEPROM and FLASH. > It seems like >something >like this should exist. Am I missing something obvious? Yes it really should. It's apparently not a very marketable idea for whatever reason. I think Dallas makes a converter chip to interface to a "commodity" SRAM chip, but that's only practical for many Kb of storage. National used to have some small serial RAMs in its COP4 series. Digikey lists the COP498 "RAM and Timer" but I forget how much RAM it has. I think it is serial. > >Oh, I also spoke with a Microchip tech support guy who told me he's >had >the same problem and was also unable to find a solution. Why not replace the PIC with one having more RAM, especially if you only need 64 bytes there are several possibilites. The PIC 16C622 or PIC16C558 offer 128 bytes RAM in an 18-pin size. Since Microchip may be listening, I'm still lobbying for a PIC with about 2K of SRAM built in. The SRAM can be a peripheral module, accessed via SFR's for address and data. There should be two sets of address and data SFRs to allow working in two places in the RAM at once. It would be nice if the address SFR had auto-increment and/or decrement capability. _____________________________________________________________________ You don't need to buy Internet access to use free Internet e-mail. Get completely free e-mail from Juno at http://www.juno.com Or call Juno at (800) 654-JUNO [654-5866]