Motorola MPC823e - Page 921

Communication Processor Module
MOTOROLA MPC823e REFERENCE MANUAL 16-467
I
2
C
COMMUNICATION
16
PROCESSOR MODULE
16.13.6 The I
2
C Buffer Descriptor Ring
The data associated with the I
2
C controller is stored in buffers, which are referenced by
buffer descriptors organized in a buffer descriptor ring located in the dual-port RAM. This
ring has the same basic configuration as the serial communication and serial management
controllers.
The buffer descriptor ring forms a circular queue that helps you organize the buffers you
want to transmit or receive. Using the buffer descriptors, the communication processor
module confirms reception and transmission or indicates error conditions so that the
processor knows the buffers have been serviced. The actual buffers can reside in either
external or internal memory and the data buffers can reside in the parameter RAM area of
another controller if it is not enabled.
Figure 16-132. I
2
C Memory Format
FRAME STATUS
DATA LENGTH
DATA POINTER
FRAME STATUS
DATA LENGTH
DATA POINTER
TX DATA BUFFER
POINTER TO I2C
RX RING
RX DATA BUFFER
DUAL-PORT RAM EXTERNAL MEMORY
TX BUFFER DESCRIPTOR RING
RX BUFFER DESCRIPTOR RING
TX DATA BUFFER
POINTER TO I2C
TX RING