C511 datasheet(64/128 Pages) SIEMENS

64 / 128 page

On-Chip Peripheral Units

Semiconductor Group

6-31

6.3.3.1 Using Timer 1 to Generate Baud Rates

When timer 1 is used as the baud rate generator, the baud rates in modes 1 and 3 are determined

by the timer 1 overflow rate and the value of SMOD as follows:

Modes 1,3 baud rate = 2SMOD/32

×(timer 1 overflow rate)

The timer 1 interrupt should be disabled in this application. The timer itself can be configured for

either "timer" or "counter" operation, and in any of its 3 running modes. In the most typical

applications, it is configured for "timer" operation, in the auto-reload mode (high nibble of

TMOD=0010B). In that case, the baud rate is given by the formula

Modes 1,3 baud rate = (2SMOD/32

) × (f

OSC/(12×(256–TH1)))

One can achieve very low baud rates with timer 1 by leaving the timer 1 interrupt enabled, and

configuring the timer to run as a 16-bit timer (high nibble of TMOD = 0001B), and using the timer 1

interrupt to do a 16-bit software reload.

Table 6-7 lists commonly used baud rates and how they can be obtained from timer 1.

Table 6-7

Timer 1 Generated Commonly Used Baud Rates

Baud Rate

OSC

SMOD

Timer 1

C/T

Mode

Reload

Value

Mode 0 max: 640 kHz

Mode 2 max: 240 K

Modes 1, 3: 40 K

19.2 K

9.6 K

4.8 K

2.4 K

1.2 K

Mode 0 max : 1 MHz

Mode 2 max : 375 K

Mode 1,3 : 62.5 K

19,2 K

9.6 K

4.8 K

2.4 K

1.2 K

110

7.68 MHz

12 MHz

11.059 MHz

6 MHz

12 MHz

FFH

FEH

FCH

F8H

EAH

FFH

FDH

FAH

F4H

E8H

72H

FEEBH

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