Freescale Semiconductor PowerQUICC MPC885 Reference Manual page 893

2
32.6 I C Commands
2
The I C transmit and receive commands, shown in
(CPCR).
Command
Initializes all transmit parameters in the parameter RAM to their reset state. Should be issued only
INIT TX
when the transmitter is disabled. The
PARAMETERS
reset both the Tx and Rx parameters.
Forces the I
CLOSE RXBD
data. If the controller is not receiving data, no action is taken. Use this command to extract data from
a partially full buffer.
Initializes all receive parameters in the parameter RAM to their reset state. Should be issued only
INIT RX
when the receiver is disabled. The
PARAMETERS
both the Tx and Rx parameters.
2
32.7 I C Buffer Descriptor (BD) Tables
As shown in Figure 32-12, buffer descriptors (BDs) are organized into separate Rx and TxBD tables in
dual-port RAM. The tables have the same basic configuration as for the SCCs and SMCs and form circular
queues that determine the order buffers are transferred. The CPM uses BDs to confirm reception and
transmission or to indicate error conditions so that the core knows buffers have been serviced. The buffers
themselves can be placed in external memory or in any unused parameter area of the dual-port RAM.
Dual-Port RAM
Tx Buffer
I2C TxBD Table
I2C RxBD Table
I2C RxBD Table Pointer
(RBASE)
I2C TxBD Table Pointer
(TBASE)
Freescale Semiconductor
Table
2
Table 32-8. I C Transmit/Receive Commands
INIT TX AND RX PARAMETERS
2
C controller to close the current Rx BD and use the next BD for subsequently received
INIT TX AND RX PARAMETERS
TxBD Table
Status and Control
Data Length
Buffer Pointer
RxBD Table
Status and Control
Data Length
Buffer Pointer
2
Figure 32-12. I C Memory Structure
MPC885 PowerQUICC Family Reference Manual, Rev. 2
32-8, are issued to the CPM command register
Description
command can also be used to
command can also be used to reset
External Memory
2
I C Controller
Tx Buffer
Rx Buffer
32-11