MPC823 datasheet(23/74 Pages) MOTOROLA

23 / 74 page

Communication Processor Module

MOTOROLA

MPC823 REFERENCE MANUAL

16-401

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 SMCx 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 must

transmit from this buffer descriptor data buffer. However, it is never modified by the

communication processor module. Normally, this value must 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 SMCx UART character is greater than 8, then the data length

must be even. For example, to transmit three UART characters of 8-bit data, 1 start, and

1 stop, the DATA LENGTH field must be initialized to 3. However, to transmit three SMCx

UART characters of 9-bit data, 1 start, and 1 stop, the DATA LENGTH field must 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 SMCx 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.

MPC823 датащи(PDF) 23 Page - Motorola, Inc