C508_01 Datasheet, PDF (81/267 Pages) Infineon Technologies AG – 8-Bit CMOS Microcontroller

C508
On-Chip Peripheral Components
6.2
Timers/Counters
The C508 contains three 16-bit timers/counters, Timer 0, Timer 1 and Timer 2. They are
useful in many applications for timing and counting.
In its “timer” function, the timer register is incremented every machine cycle. Thus, it can
be thought of as counting machine cycles. Since a machine cycle consists of three
oscillator periods, the counter rate is 1/3 of the oscillator frequency.
In its “counter” function, the timer register is incremented in response to a 1-to-0
transition (falling edge) at its corresponding external input pin, T0 or T1 (alternate
functions of P3.4 or P3.5 respectively). In this function, the external input is sampled
during S5P2 of every machine cycle. When the samples show a high in one cycle and a
low in the next cycle, the count is incremented. The new count value appears in the
register during S3P1 of the cycle following the one in which the transition was detected.
Since it takes two machine cycles (six oscillator periods) to recognize a transition from
1-to-0, the maximum count rate is 1/6 of the oscillator frequency. There are no
restrictions on the duty cycle of the external input signal, but to ensure that a given level
is sampled at least once before it changes, it must be held for at least one full machine
cycle.
6.2.1 Timer/Counter 0 and 1
Timer/counter 0 and 1 of the C508 are fully compatible with timer/counter 0 and 1 of the
C501 and can be used in the same four operating modes:
Mode 0: 8-bit timer/counter with a divide-by-32 prescaler
Mode 1: 16-bit timer/counter
Mode 2: 8-bit timer/counter with 8-bit auto-reload
Mode 3: Timer/counter 0 is configured as one 8-bit timer/counter and one 8-bit timer.
Timer/counter 1 in this mode holds its count. The effect is the same as setting
TR1 = 0.
External inputs INT0 and INT1 can be programmed to function as a gate for timer/
counters 0 and 1 to facilitate pulse width measurements.
Each timer consists of two 8-bit registers: TH0 and TL0 for timer/counter 0, TH1 and TL1
for timer/counter 1. These may be combined into one timer configuration depending on
the mode that is established. The functions of the timers are controlled by two Special
Function Registers TCON and TMOD.
In the following descriptions, the symbols TH0 and TL0 are used to specify the high-byte
and the low-byte of Timer 0 (TH1 and TL1 for timer 1, respectively). The operating modes
are described and shown for Timer 0. If not explicitly noted, this applies also to Timer 1.
User’s Manual
6-16
2001-05