Motorola MPC823e - Page 925

Communication Processor Module
MOTOROLA MPC823e REFERENCE MANUAL 16-471
I
2
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 I
2
C controller writes these bits after the received data is
placed into the associated data buffer. The actual amount of memory allocated for this buffer
must be greater than or equal to the MRBLR entry.
RX DATA BUFFER POINTER
This field always points to the first location of the associated data buffer. It must be even and
can reside in internal or external memory. The I
2
C controller writes these bits after the
received data is placed into the associated data buffer.
16.13.7.3 I
2
C TRANSMIT BUFFER DESCRIPTOR. Data to be transmitted with the I
2
C 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 must 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 must 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 LS 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, but you must clear them before submitting the buffer descriptor to the
communication processor module.