MPC823 datasheet(59/74 Pages) MOTOROLA

59 / 74 page

Communication Processor Module

MOTOROLA

MPC823 REFERENCE MANUAL

16-437

Bits 0–2—Reserved

These bits are reserved and must be set to 0.

BO—Byte Ordering

You must set these bits to select the required byte ordering of the data buffer. If this bit

field is modified on-the-fly, it takes effect at the beginning of the next frame or at the

beginning of the next buffer descriptor.

00 =

The DEC/Intel convention is used for byte ordering (swapped operation) and

is also called little-endian byte ordering. The transmission order of bytes within

a buffer word is reversed in comparison to the Motorola mode. This mode is

supported only for 32-bit port size memory.

01 =

PowerPC little-endian byte ordering. As data is transmitted onto the serial line

from the data buffer, the least-significant byte of the buffer double-word

contains data to be transmitted earlier than the most-significant byte of the

same buffer double-word.

1X = Motorola byte ordering (normal operation) is also called big-endian byte

ordering. As data is transmitted onto the serial line from the data buffer, the

most-significant byte of the buffer word contains data to be transmitted earlier

than the least-significant byte of the same buffer word.

AT—Address Type 1–3

These bits contain the function code value used during the SDMA channel memory

access. AT0 is driven with a 1 to identify this SDMA channel access as a DMA-type

access.

• MRBLR—The serial peripheral interface has one maximum receive buffer length entry

to define its receive buffer length and it defines the maximum number of bytes that the

MPC823 writes to a receive buffer on the serial peripheral interface before moving to

the next buffer. The MPC823 can write fewer bytes to the buffer than the MRBLR value

if an error or end-of-frame occurs, but it never writes more bytes than the MRBLR value.

Buffers you supply for the MPC823 to use must always be at least as long as MRBLR.

The transmit buffers for a serial peripheral interface are not affected by the value you

program into MRBLR and they can have different lengths, as needed. You can choose

the number of bytes to be transmitted by programming the DATA LENGTH field in the

TX buffer descriptor.

Note:

The MRBLR is not intended to be dynamically changed while a serial

management controller is operating. However, if it is modified in a single bus

cycle with one 16-bit move (not two 8-bit bus cycles back-to-back), then a

dynamic change in the receive buffer length can be successfully achieved. This

occurs when the communication processor module transfers control to the next

RX buffer descriptor in the table. Thus, a change to MRBLR does not have an

immediate effect. To guarantee that the change occurs on a particular RX buffer

descriptor, you must only change the MRBLR while the SMCx receiver is

disabled. The value of MRBLR must be greater than zero and it must be even if

the character length of the data is greater than 8 bits.

MPC823 Datasheet(PDF) 59 Page - Motorola, Inc

MPC823 Datasheet(HTML) 59 Page - Motorola, Inc

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