MPC823 datasheet(39/74 Pages) MOTOROLA

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Communication Processor Module

MOTOROLA

MPC823 REFERENCE MANUAL

16-417

16.11.7.11 SMCx TRANSPARENT TRANSMIT BUFFER DESCRIPTOR. Data is sent to

the communication processor module for transmission on an SMCx channel by arranging it

in buffers referenced by the channel’s transmit (TX) buffer descriptor table. Using the buffer

descriptors, the communication processor module confirms transmission or indicates error

conditions so that the processor knows the buffers have been serviced.

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

condition is encountered.

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, 7–13, and 15—Reserved

These bits are reserved and must be set to 0.

W—Wrap (Final Buffer Descriptor in Table)

0 = This is not the last buffer descriptor in the TX buffer descriptor table.

1 = This is the last buffer descriptor in the TX buffer descriptor table. After this buffer is

used, the communication processor module receives incoming data into the first

buffer descriptor that TBASE points to in the table. The number of TX buffer

descriptors in this table is programmable and determined by the W bit and overall

space constraints of the dual-port RAM.

I—Interrupt

0 = No interrupt is generated after this buffer is serviced.

1 = The TX and TXE bits in the SMCE–Transparent register are set when this buffer is

serviced. TX and TXE can cause interrupts if they are enabled.

OFFSET + 0

RES

RESERVED

RES

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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