C515C_9711 Datasheet, PDF (118/268 Pages) Siemens Semiconductor Group – 8-Bit CMOS Microcontroller

On-Chip Peripheral Components
C515C
6.3.3.3.2 Using Timer 1 to Generate Baud Rates
In mode 1 and 3 of the serial port also timer 1 can be used for generating baud rates. Then the baud
rate is determined by the timer 1 overflow rate and the value of SMOD as follows:
Mode 1, 3 baud rate =
2^SMOD
32
× (timer 1 overflow rate)
The timer 1 interrupt is usually disabled in this application. Timer 1 itself can be configured for either
"timer" or "counter" operation, and in any of its operating modes. In most typical applications, it is
configured for "timer" operation in the auto-reload mode (high nibble of TMOD = 0010B). In this
case the baud rate is given by the formula:
2^SMOD × oscillator frequency
Mode 1, 3 baud rate =
32 × 6 × (256 – (TH1))
Very low baud rates can be achieved with timer 1 if leaving the timer 1 interrupt enabled,
configuring the timer to run as 16-bit timer (high nibble of TMOD = 0001B), and using the timer 1
interrupt for a 16-bit software reload.
Semiconductor Group
6-55
1997-11-01