ST72340 datasheet(105/191 Pages) STMICROELECTRONICS

105 / 191 page

ST72340, ST72344, ST72345

105/191

SCI SERIAL COMMUNICATION INTERFACE (Cont’d)

11.5.4.4 Conventional 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 SCP[1:0] bits)

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

(see SCT[2:0] bits)

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

(see SCR[2:0] bits)

All these bits are in the SCIBRR register.

Example: If fCPU is 8 MHz (normal mode) and if

PR = 13 and TR = RR = 1, the transmit and re-

ceive baud rates are 38400 baud.

Note: The baud rate registers MUST NOT be

changed while the transmitter or the receiver is en-

abled.

11.5.4.5 Extended Baud Rate Generation

The extended prescaler option gives a very fine

tuning on the baud rate, using a 255 value prescal-

er, whereas the conventional Baud Rate Genera-

tor retains industry standard software compatibili-

ty.

The extended baud rate generator block diagram

is shown in Figure 3.

The output clock rate sent to the transmitter or to

the receiver is the output from the 16 divider divid-

ed by a factor ranging from 1 to 255 set in the SCI-

ERPR or the SCIETPR register.

Note: The extended prescaler is activated by set-

ting the SCIETPR or SCIERPR register to a value

other than zero. The baud rates are calculated as

follows:

with:

ETPR = 1, ..., 255 (see SCIETPR register)

ERPR = 1, ..., 255 (see SCIERPR register)

11.5.4.6 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:

None of the reception status bits can be set.

All the receive interrupts are inhibited.

A muted receiver can be woken up in 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.

A receiver wakes-up by Idle Line detection when

the Receive line has recognized an Idle Frame.

Then the RWU bit is reset by hardware but the

IDLE bit is not set.

A receiver wakes-up by Address Mark detection

when it received a “1” as the most significant bit of

a word, thus indicating that the message is an ad-

dress. The reception of this particular word wakes

up the receiver, resets the RWU bit and sets the

RDRF bit, which allows the receiver to receive this

word normally and to use it as an address word.

Tx =

(16*PR)*TR

fCPU

Rx =

(16*PR)*RR

fCPU

Tx =

16*ETPR*(PR*TR)

fCPU

Rx =

16*ERPR*(PR*RR)

fCPU

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