On Sun, 20 Dec 1998 15:39:34 +0000 White Horse Design writes: >At 11:45 20/12/98 , Mark J Anstice wrote: > >>I have a (common?) question. I need to interface a PIC with a RAM >chip. The > >I do this with a 16C74 (has a uart) to a 128kbyte SRAM though it has >enough >i/o lines to address a higher capacity part. > As previously mentioned, I'm using the Dallas RamPort chips to get 2 Kybytes of ram added to a 16c74a. I use the normal RamPort in some products and the battry backed one in others. I'm now looking at going with a 128 Kbyte external battery backed RAM on the 16c74a without chewing up all the I/O pins. Since serial SRAMs don't seem to be available, I WAS considering using shift registers to clock out the address and another 8 pins for data I/O. As someone on the list pointed out, since I have the 8 bit "databus", I may as well use it for everything. So, current plan is to put a couple octal latches on the same pins connected to the RAM data lines. A couple more PIC pins will act as "chip selects" for these, and I can then output a 16 bit address. I can also hang an LCD module on the same databus. I think there's a limit to how much we can economically expand a microcontroller. Again, the ideal design has zero parts, and it'd be great to have micro designs with one part: the microcontroller. Piling a bunch of stuff around it, we may as well go to a microprocessor instead of a microcontroller. At some point, this becomes a lower cost approach. Want more ROM? Hang it on the bus! Want more RAM? Hang it on the bus! Want more I/O? Hang it on the bus! Harold ___________________________________________________________________ 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/getjuno.html or call Juno at (800) 654-JUNO [654-5866]