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1 setting the baud rate, V = [ f / b ] - 1, Calculating the baud rate – FUJITSU MB91460 SERIES FR60 User Manual

Page 659: Example of calculation, F / ( v + 1), here it is: 16

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Chapter 32 USART (LIN / FIFO)

6.USART Baud Rates

Figure 6-1 Baud rate selection circuit (reload counter)

6.1 Setting the Baud Rate

This section describes how the baud rates are set and the resulting serial clock frequency is calculated.

Calculating the baud rate

The both 15-bit Reload Counters are programmed by the Baud Rate Generator Registers 1 and 0 (BGR14,
04). The following calculation formula should be used to set the wanted baud rate:

Reload Value:

v = [F / b] - 1

,

where F is the resource clock (CLKP), b the baud rate and [ ] gaussian brackets (mathematical rounding
function).

Example of Calculation

If the CPU clock is 16 MHz and the desired baud rate is 19200 baud then the reload value v is:

v = [16

*

10

6

/ 19200] - 1 = 832

The exact baud rate can then be recalculated: b

exact

= F / (v + 1), here it is: 16

*

10

6

/ 833 = 19207.6831

(Note)

Setting the reload value to 0 stops the reload counter.

(Note)

The minimum recommended division ratio is 4 (i.e. reload value is 3) due to RX oversampling filter in
asynchronous communication modes (mode 0,1 and 3).

Internal data bus

EXT

REST

BGR14

register

BGR04

register

BGR7

BGR10
BGR9
BGR8

BGR6
BGR5

BGR4

BGR3
BGR2
BGR1
BGR0

16-bit Reload Counter

Txc = 0?

Txc = v/2?

Reload

Count Value: Txc

Reload Value: v

REST

(external

set

reset

clock

OTO

1

0

1

0

BGR13
BGR12
BGR11

BGR14

Transmission

16-bit Reload Counter

Reception

FF

Rxc = 0?

Rxc = v/2?

Reload

set

reset

FF

EXT

OTO

1

0

Reload Value: v

Start bit falling

Reception
Clock

Transmission
Clock

CLK

input)

SMR04

register

SCK04

edge detected