C511_1 Datasheet, PDF (57/128 Pages) Siemens Semiconductor Group – 8-Bit CMOS Microcontroller

On-Chip Peripheral Units
6.2.2.1 Auto-Reload Mode (Up or Down Counter)
Timer 2 can be programmed to count up or down when configured in its 16-bit auto-reload mode.
This feature is invoked by a bit named DCEN (Down Counter Enable), which is located in SFR
T2MOD. When DCEN is set, timer 2 can count up or down depending on the value of pin T2EX
(P1.1).
Special Function Register T2MOD (Address C9H)
MSB
Bit No. 7
6
5
4
3
2
C9H
–
–
–
–
–
–
Reset Value : XXXXXXX0B
LSB
1
0
– DCEN T2MOD
Bit
–
DCEN
Function
Not implemented, reserved for future use.
When set, this bit allows timer 2 to be configured as an up/down counter. With
T2EX=0 down-counting is selected, with DCEN=1 up-counting is enabled.
Figure 6-23 shows timer 2 automatically counting up when DCEN=0. In this mode there are two
options selectable by bit EXEN2 in SFR T2CON.
Figure 6-23
Timer 2 Auto-Reload Mode (DCEN = 0)
Semiconductor Group
6-24