ST72325AR7-Auto datasheet(147/243 Pages) STMICROELECTRONICS

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ST72325xxx-Auto

Serial communications interface (SCI)

Doc ID 13770 Rev 3

147/243

Conventional baud rate generation

The baud rate 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

receive baud rates are 38400 baud.

Note:

The baud rate registers MUST NOT be changed while the transmitter or the receiver is

enabled.

Extended baud rate generation

The extended prescaler option provides a very fine tuning of the baud rate, using a 255

value prescaler, whereas the conventional baud rate generator retains industry standard

software compatibility.

The extended baud rate generator block diagram is described in the Figure 66.

The output clock rate sent to the transmitter or to the receiver is the output from the 16

divider divided by a factor ranging from 1 to 255 set in the SCIERPR or the SCIETPR

Note:

The extended prescaler is activated by setting 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)

Receiver muting and wake-up feature

In multiprocessor configurations it is often desirable 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 cannot be set.

●

All the receive interrupts 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

Tx =

(16*PR)*TR

fCPU

Rx =

(16*PR)*RR

fCPU

Tx =

16*ETPR*(PR*TR)

fCPU

Rx =

16*ERPR*(PR*RR)

fCPU

ST72325AR7-Auto Datasheet(PDF) 147 Page - STMicroelectronics

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