
MOTOROLA
Chapter 33. I
2
C Controller
33-11
Part V. The Communications Processor Module
Figure 33-11 shows the RFCR/TFCR bit Telds.
Table 33-7 describes the RFCR/TFCR bit Telds.
33.6 I
2
C Commands
The I
2
C transmit and receive commands, shown in Table 33-8, are issued to the CPM
command register (CPCR).
33.7 I
2
C Buffer Descriptor (BD) Tables
As shown in Figure 33-12, buffer descriptors (BDs) are organized into separate Rx and
TxBD tables in dual-port RAM. The tables have the same basic conTguration as for the
Bit
0
1
2
3
4
5
6
7
Field
BO
AT[1D3]
Reset
0000_0000
R/W
R/W
Addr
I2C Base + 04 (RFCR)/I2C Base + 05 (TFCR)
Figure 33-11. I
2
C Function Code Registers (RFCR/TFCR)
Table 33-7. RFCR/TFCR Field Descriptions
Bits
Name
Description
0D2
Reserved, should be cleared.
3D4
BO
Byte ordering. Set BO to select the required byte ordering for the buffer. If BO is changed on-the-y, it
takes effect at the beginning of the next frame (Ethernet, HDLC, and transparent) or at the beginning
of the next BD. See Appendix A, òByte Ordering.ó
00 Reserved
01 PowerPC little-endian.
1x Big-endian or true little-endian.
5D7
AT[1D3]
Address type 1D3. Contains the user-deTned function code value used during the SDMA channel
memory access. AT0 is always driven high to identify this channel access as a DMA-type access.
Table 33-8. I
2
C Transmit/Receive Commands
Command
Description
INIT
TX
PARAMETERS
Initializes all transmit parameters in the parameter RAM to their reset state. Should be issued only
when the transmitter is disabled. The
INIT
TX
AND
RX
PARAMETERS
command can also be used to reset
both the Tx and Rx parameters.
CLOSE
RXBD
Forces the I
2
C controller to close the current Rx BD and use the next BD for subsequently received
data. If the controller is not receiving data, no action is taken. Use this command to extract data from a
partially full buffer.
INIT
RX
PARAMETERS
Initializes all receive parameters in the parameter RAM to their reset state. Should be issued only when
the receiver is disabled. The
INIT
TX
AND
RX
PARAMETERS
command can also be used to reset both the
Tx and Rx parameters.