ST72561 datasheet(130/262 Pages) STMICROELECTRONICS

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ST72561

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SCI

 SERIAL COMMUNICATION INTERFACE (SCI Mode) (Cont’d)

10.7.5.4 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 en-

abled.

10.7.5.5 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 described in Figure 79.

The output clock rate sent to the transmitter or to

the receiver will be the output from the 16 divider

divided by a factor ranging from 1 to 255 set in the

SCIERPR 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)

Tx =

(16*PR)*TR

fCPU

Rx =

(16*PR)*RR

fCPU

Tx =

16*ETPR*(PR*TR)

fCPU

Rx =

16*ERPR*(PR*TR)

fCPU

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