Motorola MPC823e Reference Manual page 865

16.11.7.4 USING THE SMSYNx PIN FOR SYNCHRONIZATION. The SMSYNx pin offers
a method to externally synchronize a SMCx Transparent channel. This method differs
somewhat from the synchronization options available in the serial communication
controllers and must be studied carefully. See Figure 16-120 for an example.
Once the REN bit is set in the SMCMR, the first rising edge of the SMCLK signal that finds
the SMSYNx pin low causes the SMCx receiver to achieve synchronization. Data starts
being received or latched on the same rising edge of SMCLK that latched SMSYNx. This is
the first bit of data received. The receiver never loses synchronization again, regardless of
the state of SMSYNx, until you clear the REN bit.
Once the TEN bit is set in the SMCMR, the first rising edge of the SMCLK signal that finds
the SMSYNx pin low causes the SMCx transmitter to achieve synchronization. The SMCx
transmitter begins transmitting ones asynchronously from the falling edge of SMSYNx. After
one character of ones is transmitted, if the transmit FIFO is loaded (the transmit buffer
descriptor is ready with data), data starts being transmitted on the next falling edge of
SMCLK after some multiple of all-ones (preamble) characters are transmitted. If the transmit
FIFO is loaded at some later time, the data starts transmitting after some multiple number
of all-ones characters is transmitted.
Note: Regardless of whether the transmitter or receiver uses the SMSYNx signal, it
must make glitch-free transitions from high to low or low to high. Glitches on
SMSYNx can cause a serial management controller to behave erratically.
The transmitter never loses synchronization again, regardless of the state of SMSYNx, until
you clear the TEN bit or issue the ENTER HUNT MODE command.
MOTOROLA MPC823e REFERENCE MANUAL
Communication Processor Module
16-411