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SYNCHRONOUS SERIAL I/O (SSIO) PORT
Load SSIO x _BUF
Receive Byte
Pull SC Pin Low
SC x Pin High
No
?
SSIO x _BUF
Yes
Read
No
?
Transmit Byte
Yes
Set SSIO x Interrupt
Float SC x Pin
Pending Bit
SSIO Transmit Handshaking
SSIO Receive Handshaking
A0232-03
Figure 8-4. SSIO Handshaking Flow Diagram
8.4.2
SSIO Handshaking Operation
When handshaking is enabled, the slave pulls its clock input (SCx) low whenever it is busy. (In
receive mode, the slave is busy when the buffer is full; in transmit mode, the slave is busy when
the buffer is empty.) This happens automatically one to two state times after the rising clock edge
corresponding to the last data bit of the transmitted 8-bit packet. The slave releases its SCx line
only after the CPU reads from or writes to SSIOx_BUF, which clears the transmit buffer status
(TBS) bit in SSIOx_CON and indicates that SSIOx_BUF is available for another packet to be re-
ceived or transmitted.
When handshaking is enabled, the master leaves its clock output (SCx) high at the end of each
byte transfer. This allows the slave to pull the clock line low if its SSIOx_BUF register is unavail-
able for the next transfer. The master waits for the clock line to return high before it attempts the
next transfer. (If handshaking is not enabled for the master, the master drives the clock line low
between transfers.)
8-7
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