MPC823 datasheet(60/74 Pages) MOTOROLA

60 / 74 page

Communication Processor Module

16-438

MPC823 REFERENCE MANUAL

MOTOROLA

• 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 idle 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 must

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 idle 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 must

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

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 DATA LENGTH field of the

TX buffer descriptor 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 the serial

channel parameter RAM to their reset state and must 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 must 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, issue the CLOSE RX BD command.

MPC823 Datasheet(PDF) 60 Page - Motorola, Inc

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