Sam Coupe Scrapbook

Technical Section
- I/O Ports

Information provided by: Andrew Gale

If you want just a few i.o ports for your own projects then you can save yourself a chip or so (and a fair bit of soldering) by making use of the PRINTL signal on the euroconnector. This signal is normally high and goes low when IORQL is low (ie the SAM is trying to input or output some data) and the address is in the range 232 to 239 - this is the area reserved for the printer and serial interface. If you just use a parallel printer, then you can select your device when PRINTL is low and A2 is high - then you have ports 236, 237, 238 and 239 to play with (by looking at A0 and A1). IF you just need two i/o ports then you could select your circuit when PRINTL is low, A2 is low and A1 is high - then you've got ports 234 and 235 (looking at A0). These two ports are reserved for the second parallel printer, but most people on have one (and use ports 232 and 233 to drive it). There was a version of the parallel printer interface which used a PIA - and I don't know how many ports it uses, so beware!

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