MPC823 datasheet(70/74 Pages) MOTOROLA

70 / 74 page

Communication Processor Module

16-448

MPC823 REFERENCE MANUAL

MOTOROLA

DATA LENGTH

This field indicates 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 is greater than zero, but if the

number of data bits in the character is greater than 8, then DATA LENGTH must be even.

For example, to transmit three characters of 8-bit data, the DATA LENGTH field must be

initialized to 3. However, to transmit three characters of 9-bit data the DATA LENGTH field

must be initialized to 6, since the three 9-bit data fields occupy three half-words in memory.

The serial peripheral interface writes these bits after it finishes transmitting the associated

data buffer.

TX DATA BUFFER POINTER

This field always points to the first location of the associated data buffer. They can be even

or odd, unless the number of actual data bits in the character is greater than 8 bits, in which

case the transmit buffer pointer must be even. The buffer can reside in internal or external

memory. The serial peripheral interface writes these bits after it finishes transmitting the

associated data buffer.

16.12.4.2 SPI COMMAND REGISTER. The 8-bit read/write SPI command (SPCOM)

STR—Start Transmit

When the serial peripheral interface is configured as a master, setting this bit to 1 causes

the serial peripheral interface to start transmitting and receiving data to and from the

transmit/receive buffers if they are ready. When the serial peripheral interface is in slave

mode, setting the STR bit to 1 when the serial peripheral interface is idle causes the serial

peripheral interface to load the transmit data register from the SPI transmit buffer and start

transmission as soon as the next SPI input clocks and select signal are received. This bit is

automatically cleared after one system clock cycle.

Bits 1–7—Reserved.

These bits are reserved and must be set to 0.

SPCOM

BIT

FIELD

STR

RESERVED

RESET

R/W

ADDR

(IMMR & 0xFFFF0000) + 0xAAD

MPC823 Datasheet(PDF) 70 Page - Motorola, Inc