26/10/2004 14:10:36, "Glen VanMilligan" wrote: > Hi, > I'm needing to add 24 I/O ports to the Mother board, but being a new > user, > > I'm not sure what lines I can use to add a device like an 8255 ( > or similar ). > Can you offer some suggestions to do this? I wouldn't go to the lengths of using an 8255 - it would be much easier to use the LCD GPIOs, if you're not using all of them for LCD purposes, and use 4 or 8 of them as a little data bus, some more as addresses and strobes, and latch your 24 IO bits that way. Do you want each of your 24 pins to be I/O, or are some inputs, some outputs? If you need the more complex case, then building what you want out of a small Xilinx device (XCR3032 or similar) would be the way I'd approach it, to reduce the development effort. It's very rare that I use stuff like 8255s any more. (and, for what it's worth, the GPIO pins aren't 5Volt tolerant - if you plan to interface to 5V stuff, then the XCR3xxx family is exceedingly convenient, since it's 5V-tolerant, and has slew-rate control, if you need it) If you do want lots of bandwidth, though, then you'll need to use the 'real' address and data buses. (The GPIOs can be switched at many tens of MHz, though, so don't rule them out unnecessarily). This would involve a much more complex PCB, though, since you'd need to lay out for the backplane connector, rather than just using the 1.25mm pitch IO connectors. It all depends on what resources you've got, really. Steve (RIP John Peel, whose show has been the soundtrack to an awful lot of Balloon design hours)