C511 datasheet(63/128 Pages) SIEMENS

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Semiconductor Group

6-30

On-Chip Peripheral Units

6.3.3

Baud Rates

There are several possibilities to generate the baud rate clock for the serial interface depending on

the mode in which it is operated.

To clearify the terminology, something should be mentioned about the differences between "baud

rate clock" and "baud rate".

The serial interface requires a clock rate which is 16 times the baud rate for the internal

synchronization. Therefore, the baud rate generators have to 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 chapter already includes the factor and calculate the

final baud rate.

Mode 0

The baud rate in mode 0 is fixed:

Mode 0 baud rate = oscillator frequency/12 =

OSC/12

Mode 2

The baud rate in mode 2 depends on the value of bit SMOD in special function register PCON

(87H). If SMOD = 0 (which is the value on reset), the baud rate is fOSC/64. If SMOD = 1, the baud

rate is

OSC/32.

Mode 2 baud rate = 2SMOD/64

×(f

OSC)

Modes 1 and 3

The baud rates in mode 1 and 3 are determined by the timer overflow rate. These baud rates can

be determined by timer 1 or by timer 2 or by both (one for transmit and the other for receive).

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