C868_02 Datasheet, PDF (73/244 Pages) Infineon Technologies AG – 8 - Bit CMOS Microcontroller

C868
On-Chip Peripheral Components
4.6.7 Baudrate Generator Mode
The baudrate generator mode of timer/counter 2 can be selected by setting the bits
TCLK and/or RCLK in register T2CON. So the baudrate for the receive and transmit
functions can be individually controlled. The timer/counter itself functions similar to the
auto-reload mode with up/down counting is disabled. The timer/counter counts up and
overflows but the overflow condition does not set the TF2 flag. An interrupt request to the
core is not generated. Upon an overflow condition, the timer/counter registers are
reloaded with the RC2L/H registers content and continues counting as before.
The overflow signal is provided as an output of the timer/counter 2 block. This is active
for one clock cycle only. Additionally, the status of the TCLK and RCLK bits are also
provided as outputs of the timer 2 block. The UART, for e.g., could use these signals to
control its baudrates.
The main difference between the auto-reload mode and the baudrate generator mode is
that timer 2 as a baudrate generator uses f_SYS/2 as the count clock. In the auto-reload
mode the timer/counter 2 uses f_SYS/12 as the count clock.
If EXEN2=1, in the baudrate generator mode, a falling edge on pin T2EX can be used to
generate an interrupt. In this case, flag EXF2 will be set.
Note: When timer/counter 2 is in the baudrate generator mode, an increment of the timer
register happens for every other f_SYS. Therefore, software should not access the
T2L/H registers. Software may however, read the RC2L/H registers. Software
write into these registers may coincide with a timer update or reload cycle and
should therefore be avoided.
User’s Manual
4-29
V 0.4, 2002-01