
Communication Processor Module
MOTOROLA
MPC823 USER’S MANUAL
16-461
I2
C
COMMUNICATION
16
PROCESSOR
MODULE
DATA LENGTH
This field represents the number of octets that the communication processor module writes
into this buffer descriptor data buffer. The communication processor module writes it once
the buffer descriptor closes. The I2C controller writes these bits after the received data is
placed into the associated data buffer. The actual amount of memory allocated for this buffer
should be greater than or equal to the MRBLR.
RX DATA BUFFER POINTER
This field always points to the first location of the associated data buffer, must be even, and
can reside in internal or external memory. The I2C controller writes these bits after the
received data is placed into the associated data buffer.
16.13.7.3 I2C TRANSMIT BUFFER DESCRIPTOR. Data to be transmitted with the I2C is
sent to the communication processor module by arranging it in buffers referenced by the
transmit (TX) buffer descriptor ring. The first word of the TX buffer descriptor contains status
and control bits. You should prepare the following bits before transmitting data.
R—Ready
0 = The data buffer associated with this buffer descriptor is not ready for transmission.
You are free to manipulate this buffer descriptor or its associated data buffer. The
communication processor module clears this bit after the buffer is transmitted or
after an error occurs.
1 = The data buffer, which you prepare for transmission, is not transmitted yet or is
currently being transmitted. You cannot write any fields of this buffer descriptor
once this bit is set.
Bits 1 and 6–12—Reserved
These bits are reserved and should be set to 0.
0
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
OFFSET + 0
R
RES
WI
L
S
RESERVED
NAK
UN
CL
OFFSET + 2
DATA LENGTH
OFFSET + 4
TX DATA BUFFER POINTER
OFFSET + 6
NOTE:
You are only responsible for initializing the items in bold.
Note:
The communication processor module sets all the status bits in this buffer
descriptor. You should clear all the status bits before submitting the buffer
descriptor to the communication processor module. For example, the parity error
bit is only set when a parity error occurs.