C511 datasheet(61/128 Pages) SIEMENS

61 / 128 page

Semiconductor Group

6-28

On-Chip Peripheral Units

6.3.1 Multiprocessor Communications

Modes 2 and 3 have a special provision for multiprocessor communications. In these modes, 9 data

bits are received. The 9th data bit goes into RB8. Then comes a stop bit. The port can be

programmed such that when the stop bit is received, the serial port interrupt will be activated only

if RB8 = 1. This feature is enabled by setting bit SM2 in SCON. A way to use this feature in

multiprocessor systems is as follows.

When the master processor wants to transmit a block of data to one of several slaves, it first sends

out an address byte which identifies the target slave. An address byte differs from a data byte in

that the 9th bit is 1 in an address byte and 0 in a data byte. With SM2 = 1, no slave will be interrupted

by a data byte. An address byte, however, will interrupt all slaves, so that each slave can examine

the received byte and see if it is beeing addressed. The addressed slave will clear its SM2 bit and

prepare to receive the data bytes that will be coming. The slaves that weren’t being addressed leave

their SM2s set and go on about their business, ignoring the incoming data bytes.

SM2 has no effect in mode 0, and in mode 1 can be used to check the validity of the stop bit. In a

mode 1 reception, if SM2 = 1, the receive interrupt will not be activated unless a valid stop bit is

received.

C511 Datasheet(PDF) 61 Page - Siemens Semiconductor Group