C511_1 Datasheet, PDF (58/128 Pages) Siemens Semiconductor Group – 8-Bit CMOS Microcontroller

On-Chip Peripheral Units
If EXEN2 = 0, timer 2 counts up to FFFFH and then sets the TF2 bit upon overflow. The overflow
also causes the timer registers to be reloaded with the 16-bit value in RC2H and RC2L. The values
in RC2H and RC2L are preset by software.
If EXEN2 = 1, a 16-bit reload can be triggered either by an overflow or by a 1-to-0 transition at the
external input T2EX (P1.1). This transition also sets the EXF2 bit. Both the TF2 and EXF2 bits can
generate an timer 2 interrupt if enabled.
Setting the DCEN bit enables timer 2 to count up or down as shown in figure 6-24. In this mode the
T2EX pin controls the direction of count.
Figure 6-24
Timer 2 Auto-Reload Mode (DCEN = 1)
A logic 1 at T2EX makes timer 2 count up. The timer will overflow at FFFFH and set the TF2 bit.
This overflow also causes the 16-bit value in RC2H and RC2L to be reloaded into the timer
registers, TH2 and TL2, respectively.
A logic 0 at T2EX makes timer 2 count down. Now the timer underflows when TH2 and TL2 equal
the values stored in RC2H and RC2L. The underflow sets the TF2 bit and causes FFFFH to be
reloaded into the timer registers. The EXF2 bit toggles whenever timer 2 overflows or underflows.
This bit can be used as a 17th bit of resolution if desired. In this operating mode, EXF2 does not
flag an interrupt.
Semiconductor Group
6-25