MPC823 datasheet(30/74 Pages) MOTOROLA

30 / 74 page

Communication Processor Module

16-408

MPC823 REFERENCE MANUAL

MOTOROLA

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 16-118 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.

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.

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.

MPC823 데이터시트(PDF) 30 Page - Motorola, Inc