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Communication Processor Module
Synchronization can be achieved in two ways. First, when the transmitter is connected to a
TDM channel, it can be synchronized to a time-slot. Once the frame sync is received, the
transmitter waits for the first bit of its time-slot to occur before it starts transmitting. Data is
only transmitted during the time-slots defined by the time-slot assigner. Secondly, when
working with its own set of pins, the transmitter starts transmitting when the SMSYNx signal
is asserted.
When buffer descriptor data is completely written to the transmit FIFO, the L bit is checked
and if it is set, a serial management controller writes the message status bits into the buffer
descriptor and clears the R bit. It then starts transmitting idles. When the end of the current
buffer descriptor is reached and the L bit is not set, only the R bit is cleared. In both cases,
an interrupt is issued according to the I bit in the buffer descriptor. By appropriately setting
the I bit in each buffer descriptor, interrupts can be generated after each buffer, a specific
buffer, or each block is transmitted. The serial management controller then proceeds to the
next buffer descriptor in the table. If no additional buffers have been presented to the serial
management controller for transmission and the L bit was cleared, an underrun is detected
and the serial management controller begins transmitting idles.
If the CM bit is set in the transmit buffer descriptor, the R bit is not cleared, thus allowing the
associated data buffer to be automatically retransmitted next time the communication
processor module accesses this data buffer. For instance, if a single transmit buffer
descriptor is initialized with the CM bit and the W bit set, the data buffer is continuously
transmitted until you clear the R bit of the buffer descriptor.
16.11.7.3 SMCx TRANSPARENT CHANNEL RECEPTION PROCESS. When the core
enables the SMCx receiver in transparent mode, it waits for synchronization before
receiving data. Once synchronization is achieved, the receiver transfers incoming data into
memory according to the first receive buffer descriptor in the ring. Synchronization can be
achieved in two ways. First, when the receiver is connected to a TDM channel, it can be
synchronized to a time-slot. Once the frame sync is received, the receiver waits for the first
bit of its time-slot to occur before reception begins. Data is only received during the
time-slots defined by the time-slot assigner. Secondly, when working with its own set of pins,
the receiver starts receiving when the SMSYNx signal is asserted.
When the data buffer is filled, a SMCx Transparent controller clears the E bit in the buffer
descriptor and generates an interrupt if the I bit in the buffer descriptor is set. If the incoming
data exceeds the length of the data buffer, a serial management controller fetches the next
buffer descriptor in the table and, if it is empty, continues transferring data to the associated
data buffer. If the CM bit is set in the receive buffer descriptor, the E bit is not cleared, thus
allowing the associated data buffer to be automatically overwritten next time the
communication processor module accesses this data buffer.
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MPC823e REFERENCE MANUAL
MOTOROLA
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