> (1) The "Parallel Port" mode, how does it work?  Could I do bidirectional
> comms with a PC parallel port?  What would be a typical application of it?

I haven't used it (yet) but this is how I assume you would

Interface to another micro -

This could be a dynamic uC that has the in-built /RD /RW and /CS
lines, such as 8031 derivatives, AVR 90S family, something like
those, that have specific or multiplexed modes for addressing external
memories, sometimes with the addition of ALE (Address Latch Enable)
for device selection. It could be any other micro which has /RW /RD
and /CS emulated in s/w, like you could with any PIC. Because of
the 877's ability to write to its own memory, it would be possible to
write program data to it from another micro, or just use it as a very
smart memory chip

Interface to a PC -

Yes, you could make a 2-way 8-bit data exchange with a PC, as long as
the /RD /WR and /CS controls are there. This would mean using three
of the Status lines in eg LPT1: or whatever mode you have the PC in. I
think you should also be able to interface this port to the motherboard
through a card slot, but I haven't looked into it

In short, PSP is just a port like any other 8-bit port, except that it can
be
configured as an 'on demand' parallel data transmitter/receiver in the
smae way that the serial port can be

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