Motorola MPC823e Reference Manual page 875

L— Last in Message
0 = The last byte in the buffer is not the last byte in the transmitted transparent frame.
Data from the next transmit buffer (if ready) is transmitted immediately following the
last byte of this buffer.
1 = The last byte in this buffer is the last byte in the transmitted transparent frame. After
this buffer is transmitted, the transmitter requires synchronization before the next
buffer is transmitted.
CM—Continuous Mode
0 = Normal operation.
1 = The communication processor module does not clear the R bit after this buffer
descriptor is closed, thus allowing the associated data buffer to be automatically
retransmitted next time the communication processor module accesses this buffer
descriptor. However, the R bit will be cleared if an error occurs during transmission,
regardless of how the CM bit is set.
UN—Underrun
This bit indicates that a serial management controller has encountered a transmitter
underrun condition while transmitting the associated data buffer.
DATA LENGTH
This field represents the number of octets that the communication processor module must
transmit from this data buffer and it is never modified by the communication processor
module. This field can be even or odd, but if the number of bits in the transparent character
is greater than 8, this field must be even. For example, to transmit three transparent 8-bit
characters, this field must be initialized to 3. However, to transmit three transparent 9-bit
characters, this field must be initialized to 6 since the three 9-bit characters occupy three
half-words in memory.
TX DATA BUFFER POINTER
This field always points to the first byte of the associated data buffer. They can be even or
odd, unless the character length is greater than 8 bits, in which case this field must be even.
For instance, the pointer to 8-bit transparent characters can be even or odd, but the pointer
to 9-bit transparent characters must be even. The buffer can reside in internal or external
memory.
MOTOROLA MPC823e REFERENCE MANUAL
Communication Processor Module
16-421