MPC823 datasheet(56/74 Pages) MOTOROLA

56 / 74 page

Communication Processor Module

16-434

MPC823 REFERENCE MANUAL

MOTOROLA

Transmission continues until no more data is available or the SPISEL pin is negated. If the

pin is negated before all the data is transmitted, it stops, but the TX buffer descriptor stays

open. Further transmission continues once the SPISEL pin is reasserted and SPICLK

begins toggling. After the characters in the TX buffer descriptor are transmitted, the serial

peripheral interface transmits ones if SPISEL is not negated.

16.12.3.1 MULTIMASTER OPERATION. The serial peripheral interface can operate in a

multimaster environment in which more than one SPI device is connected to the same bus.

In this configuration, the SPIMOSI, SPIMISO, and SPICLK pins of all SPIs are connected

together and the SPISEL input pins are connected separately. In this environment, only one

SPI device can be in master mode and all the others must be in slave mode. When the serial

peripheral interface is configured as a master and its SPISEL signal goes active or low, a

multimaster error will occur because more than one SPI device is a bus master. The serial

peripheral interface sets the MME bit in the SPIE register and a maskable interrupt is issued

to the core. It also disables SPI operation and the output drivers of the SPI pins. The core

must clear the EN bit the SPMODE register before using the serial peripheral interface

again. After the problems are corrected, clear the MME bit and enable the serial peripheral

interface the same way you would after a reset.

Note: The maximum sustained data rate that the serial peripheral interface supports is

SYSTEMCLK/50. However, the serial peripheral interface can transfer a single

character at much higher rates. For instance, SYSTEMCLK/4 in master mode

and SYSTEMCLK/2 in slave mode. If multiple characters are to be transmitted,

you must insert gaps between them so that it will not exceed the maximum

sustained data rate.

MPC823 Datasheet(PDF) 56 Page - Motorola, Inc