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Communication Processor Module
16-394
MPC823 USER’S MANUAL
MOTOROLA
SMC
COMMUNICATION
16
PROCESSOR
MODULE
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.
CM—Continuous Mode
0 = Normal operation.
1 = The R bit is not cleared by the communication processor module 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.
P—Preamble
0 = No preamble sequence is sent.
1 = The SMC UART controller sends one all-ones character before it sends the data
so that the other end detects an idle line before the data is received. If this bit is set
and the data length of this buffer descriptor is zero, only a preamble is sent.
DATA LENGTH
This field represents the number of octets that the communication processor module should
transmit from this buffer descriptor data buffer. However, it is never modified by the
communication processor module. Normally, this value should be greater than zero, but it
can be equal to zero with the P bit set if only a preamble is sent.
If the number of data bits in the SMC UART character is greater than 8, then the data length
should be even. For example, to transmit three UART characters of 8-bit data, 1 start, and
1 stop, the DATA LENGTH field should be initialized to 3. However, to transmit three SMC
UART characters of 9-bit data, 1 start, and 1 stop, the DATA LENGTH field should be
initialized to 6, since the three 9-bit data fields occupy three half-words in memory (the 9
least-significant bits of each half-word).
TX DATA BUFFER POINTER
This field always points to the first location of the associated data buffer. It can be even or
odd, unless the number of actual data bits in the SMC UART character is greater than 8 bits,
in which this field is even. For instance, the pointer to 8-bit data, 1 start, and 1 stop
characters can be even or odd, but the pointer to 9-bit data, 1 start, and 1 stop characters
must be even. The buffer can reside in internal or external memory.