MPC823 datasheet(22/74 Pages) MOTOROLA

22 / 74 page

Communication Processor Module

16-400

MPC823 REFERENCE MANUAL

MOTOROLA

16.11.6.12 SMCx UART 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 ring. 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,

but you are free to manipulate this buffer descriptor or its associated data buffer.

The communication processor module clears this bit after the buffer has been

transmitted or 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, 4–5, and 8–15—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 only 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 bit in the SMCE–UART register is set when this buffer is serviced.

Transmission can cause an interrupt if it is enabled.

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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