SDA5250 Datasheet, PDF (94/143 Pages) Siemens Semiconductor Group – TVTEXT 8-Bit Microcontroller

SDA 525x
6.3.10.2 Baud Rates
The baud rate in mode 0 is fixed:
Mode 0 baud rate = -^f---^O--6--^S----^C--
The baud rate in mode 2 depends on the value of bit SMOD in special function register
PCON (bit 7). If SMOD = 0 (which is the value on reset), the baud rate is 1/32 of the
oscillator frequency. If SMOD = 1, the baud rate is 1/16 of the oscillator frequency.
Mode 2 baud rate = ^2----S--3--^M--2--^O----^D-- × f _OSC
The baud rates in modes 1 and 3 are determined by the timer 1 overflow rate or can be
generated by the internal baud rate generator.
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:
Mode 1, 3 baud rate = ²----^S--₁--^M--₆--^O----^D-- × Time 1 overflow
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 the 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:
Mode 1, 3 baud rate = -²---^S--₁--^M--₆--^O----^D-- × ₁----₂-----_×----₍---₂-^f--₅-^O---₆-^S---Ð^C-----_T----_H-----₁---₎-
One can achieve very low baud rates with timer 1 by leaving the timer 1 interrupt
enabled, 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.
Semiconductor Group
94
1998-04-08