MPC823 datasheet(68/74 Pages) MOTOROLA

68 / 74 page

Communication Processor Module

16-446

MPC823 REFERENCE MANUAL

MOTOROLA

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

as the buffer descriptor is closed. The serial peripheral interface 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

it can reside in internal or external memory. The serial peripheral interface writes these bits

after the received data is placed into the associated data buffer.

16.12.4.1.3 SPI Transmit Buffer Descriptor. Data to be transmitted by the serial

peripheral interface 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

and you are free to manipulate it 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, 5, and 7–13—Reserved

These bits are reserved and must be set to 0.

OFFSET + 0

RES

RESERVED

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.

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