ST72C171 datasheet(83/152 Pages) STMICROELECTRONICS

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ST72C171

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SERIAL COMMUNICATIONS INTERFACE (Cont’d)

7.7.4.4 Baud Rate Generation

The baud rates for the receiver and transmitter (Rx

and Tx) are set independently and calculated as

follows:

with:

PR = 1, 3, 4 or 13 (see SCP0 & SCP1 bits)

TR = 1, 2, 4, 8, 16, 32, 64,128

(see SCT0, SCT1 & SCT2 bits)

RR = 1, 2, 4, 8, 16, 32, 64,128

(see SCR0,SCR1 & SCR2 bits)

All these bits are in the BRR register.

Example: If fCPU is 8 MHz and if PR=13 and

TR=RR=1, the transmit and receive baud rates are

19200 bauds.

Note: The baud rate registers MUST NOT be

changed while the transmitter or the receiver is en-

abled.

7.7.4.5 Receiver Muting and Wake-up Feature

In multiprocessor configurations it is often desira-

ble that only the intended message recipient

should actively receive the full message contents,

thus reducing redundant SCI service overhead for

all non addressed receivers.

The non addressed devices may be placed in

sleep mode by means of the muting function.

Setting the RWU bit by software puts the SCI in

sleep mode:

All the reception status bits can not be set.

All the receive interrupt are inhibited.

A muted receiver may be awakened by one of the

following two ways:

– by Idle Line detection if the WAKE bit is reset,

– by Address Mark detection if the WAKE bit is set.

The Receiver wakes-up by Idle Line detection

when the Receive line has recognised an Idle

Frame. Then the RWU bit is reset by hardware but

the IDLE bit is not set.

The Receiver wakes-up by Address Mark detec-

tion when it received a “1” as the most significant

bit of a word, thus indicating that the message is

an address. The reception of this particular word

wakes up the receiver, resets the RWU bit and

sets the RDRF bit, which allows the receiver to re-

ceive this word normally and to use it as an ad-

dress word.

Tx =

(32*PR)*TR

fCPU

Rx =

(32*PR)*RR

fCPU

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