Motorola MPC823e Reference Manual page 920

Communication Processor Module
• RBPTR—The receive buffer pointer entry for each I
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 the RBPTR, it can be modified when the receiver is disabled or when you are
sure no receive buffer is currently in use.
• TBPTR—The transmit buffer pointer entry for each I
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
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 debugging
information. Additional parameters are listed in Table 16-40. RPTR and TPTR are
updated by the SDMA channels to show the next address to be accessed. TCNT is a
down-count value that is initialized with the DATA LENGTH field of the TX buffer
descriptor and decremented with every byte read by the SDMA channels. 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, TTMP, and reserved
areas can only be used by the RISC microcontroller.
16.13.5 I 2 C Commands
You can program the CPM command register (CPCR) with the following commands to
transmit or receive data.
• INIT TX PARAMETERS—This command initializes all transmit parameters in this serial
channel's 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 I
RX buffer descriptor if it is being used and to use the next buffer descriptor for any
subsequently received data. If the I
no action is taken by this command.
• INIT RX PARAMETERS—This command initializes all the receive parameters in this
serial channel's 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.
16-466
2
C controller is not in the process of receiving data,
MPC823e REFERENCE MANUAL
2
C channel points to the next buffer
2
C channel points to the next buffer
2
C controller to close the current
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