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!
