Communication Processor Module
MOTOROLA
MPC823 USER’S MANUAL
16-431
SPI
COMMUNICATION
16
PROCESSOR
MODULE
RRBPTR—The RX buffer descriptor pointer entry for each SPI channel points to the
next buffer descriptor that the receiver transfers data to when it is in an idle state or to
the current buffer descriptor during frame processing. After a reset or when the end of
the buffer descriptor table is reached, the communication processor module initializes
this pointer to the value programmed in the RBASE entry. Although in most applications
you should not write RBPTR, it can be modified when the receiver is disabled or when
you are sure that no receive buffer is currently in use.
TBPTR—The TX buffer descriptor pointer entry for each SPI channel points to the next
buffer descriptor that the transmitter transfers data from when it is in an idle state or to
the current buffer descriptor during frame transmission. After a reset or when the end
of buffer descriptor table is reached, the communication processor module initializes
this pointer to the value programmed in the TBASE entry. Although in most applications
you should not write TBPTR, it can be modified when the transmitter is disabled or when
you are sure that no transmit buffer is currently in use.
Other General Parameters—For normal operation, you do not need to access these
parameters. They are only listed here because they provide helpful information for
experienced users and they can be used for debugging purposes. Additional
parameters are listed in
Table 16-39. RPTR and TPTR are updated by the SDMA
channels to show the next address in the buffer to be accessed. TCNT is a down-count
value initialized with the TX buffer descriptor data length and decremented with every
byte read by the SDMA channels. The RCNT is a down-count value that is initialized
with the MRBLR value and decremented with every byte the SDMA channels write. The
RSTATE, TSTATE, RTMP, TMP, and reserved areas can only be used by the RISC
microcontroller.
16.12.3.3 SPI COMMANDS. The following transmit and receive commands are issued to
the CPM command register (CPCR).
INIT TX PARAMETERS—This command initializes all transmit parameters in this serial
channel parameter RAM to their reset state and should only be issued when the
transmitter is disabled. The INIT TX AND RX PARAMS command can also be used to
reset the transmit and receive parameters.
CLOSE RX BD—This command is used to force the SPI controller to close the current
RX buffer descriptor if it is currently being used and to use the next buffer descriptor for
any subsequently received data. If the SPI controller is not in the process of receiving
data, no action is taken by this command.
INIT RX PARAMETERS—This command initializes all the receive parameters in this
serial channel parameter RAM to their reset state and should only be issued when the
receiver is disabled. The INIT TX AND RX PARAMS command can also be used to
reset the receive and transmit parameters.
Note: To extract data from a partially full buffer, use the CLOSE RX BD command.