C508 datasheet(44/93 Pages) INFINEON

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C508

Data Sheet

2000-08

Baud Rate Generation

There are several possibilities to generate the baud rate clock for the serial port

depending on the mode in which it is operating.

Figure 18

Baud Rate Generation for the Serial Port

For clarification, some terms regarding the difference between “baud rate clock” and

“baud rate” should be mentioned. The serial interface requires a clock rate which is

16 times the baud rate for internal synchronization. Therefore, the baud rate generators

must provide a “baud rate clock” to the serial interface which - there divided by 16 -

results in the actual “baud rate”. However, all formulas given in the following section

already include the factor and calculate the final baud rate. Further, the abbreviation

fOSC refers to the external clock frequency (oscillator or external input clock operation).

Depending on the programmed operating mode different paths are selected for the baud

rate clock generation. Figure 18 shows the dependencies of the serial port baud rate

clock generation on the two control bits and from the mode which is selected in the

special function register SCON.

MCS04074

SCON.7/

SCON.6

(SM0/SM1)

Mode 1

Mode 3

Mode 2

Mode 0

OSC

Timer 1 Overflow

Only one mode

can be selected

PCON.7

(SMOD)

÷ 2

Baudrate

Clock

Note: The switch configuration shows the reset state

ADCON0.7

(BD)

Baudrate

Generator

(SRELH

SRELL)

÷ 6

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