68300

I have used SPI for bidirectional communications in a single master/
multiple slaves configuration. The master polls the slaves,
the communication using 7-bits (bits 0-6) of every byte.
Whatever the master sends is with bit 7 being 0, whatever the slave sends
is with bit 7 being a 1. Thus, the master can always see what got clocked
in every time it sends a byte to the slave - either what it sent last, 
if bit 7 is 0, or some output from the slave, if bit 7 is a 1. Polling
has to be limited to a rate the slaves can handle (probably they have
to do an for IRQ every byte). I have done this between a 68340 (bit-banging
the SPI) and a variable number of HC11-s. Works fine until today. 

Dimiter

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