ST72324BK datasheet(111/188 Pages) STMICROELECTRONICS

111 / 188 page

ST72324B

On-chip peripherals

111/188

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 SCI Baud Rate Register (SCIBRR) on page 120.

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 gives a very fine tuning on 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 Figure 59.

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

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 SCI Extended Transmit Prescaler Division Register (SCIETPR) on

page 121.

ERPR = 1,.. 255, see SCI Extended Receive Prescaler Division Register (SCIERPR) on

page 120.

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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