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Synchronous Serial Interface
12-7
12.3 SSI PROGRAMMING
The SSI interface allows for a variety of software and hardware protocols.
n Signaling a read/write—In general, software uses the first write to the SSI to transmit
an address or count to the peripheral. This value can include a read/write flag in the
case where the device supports both reads and writes.
n Using SSD1 as an address register—The SSD1 register can be an address register
that holds the value of the last address accessed, and the SSD0 register can be the
data transmit register. In this case, the current value in the SSD1 register can be used
by software to generate the next address or to determine if the last transaction was a
read or a write.
n Using SSD1 and SSD0 as transmit registers for two peripheral devices—In some
systems, it may clarify the code and aid in debugging to view the two data transmit
registers as unique to different peripheral devices. This allows the last value transmitted
to each device to be examined by debug code.