C515 Datasheet, PDF (25/55 Pages) Siemens Semiconductor Group – 8-Bit CMOS Microcontroller

C515
Timer / Counter 0 and 1
Timer/Counter 0 and 1 can be used in four operating modes as listed in table 4 :
Table 4
Timer/Counter 0 and 1 Operating Modes
Mode Description
0
8-bit timer/counter with a
divide-by-32 prescaler
1
16-bit timer/counter
2
8-bit timer/counter with
8-bit autoreload
3
Timer/counter 0 used as one
8-bit timer/counter and one
8-bit timer
Timer 1 stops
TMOD
M1 M0
0
0
1
1
1
0
1
1
Input Clock
internal
external (max)
f_OSC/12x32
f_OSC/24x32
f_OSC/12
f_OSC/24
In the “timer” function (C/T = ‘0’) the register is incremented every machine cycle. Therefore the
count rate is f_OSC/12.
In the “counter” function the register is incremented in response to a 1-to-0 transition at its
corresponding external input pin (P3.4/T0, P3.5/T1). Since it takes two machine cycles to detect a
falling edge the max. count rate is f_OSC/24. External inputs INT0 and INT1 (P3.2, P3.3) can be
programmed to function as a gate to facilitate pulse width measurements. Figure 9 illustrates the
input clock logic.
f _OSC
÷12
P3.4/T0
P3.5/T1
max f _OSC/24
TR 0/1
TCON
P3.2/INT0
P3.3/INT1
Gate
=1
TMOD
Figure 9
Timer/Counter 0 and 1 Input Clock Logic
C/T
TMOD
0
1
&
Control
1
MCS01768
Semiconductor Group
25
f _OSC/12
Timer 0/1
Input Clock
1997-08-01