BASIC TIMER and TIMER 0
S3C80A5B
10-6
Pulse Width Modulation Mode
Pulse width modulation (PWM) mode lets you program the width (duration) of the pulse that is output at the T0PWM
pin. As in interval timer mode, a match signal is generated when the counter value is identical to the value written to
the timer 0 data register. In PWM mode, however, the match signal does not clear the counter. Instead, it runs
continuously, overflowing at ‘FFH’, and then continues incrementing from ‘00H’.
Although you can use the match signal to generate a timer 0 overflow interrupt, interrupts are not typically used in
PWM-type applications. Instead, the pulse at the T0PWM pin is held to Low level as long as the reference data
value is
less than or equal to
(
≤
) the counter value and then the pulse is held to High level for as long as the data
value is
greater than
( > ) the counter value. One pulse width is equal to t
CLK
256 (see Figure 11-4).
Interrupt
Enable/Disable
(T0CON.1)
CTL
P2.0/
T0PWM
T0CON.5
T0CON.4
Match Signal
T0CON.3
IRQ0(T0INT)
IRQ0 (T0OVF)
CLK
Match
Data Register
Buffer Register
Comparator
Counter
T0OVF
(T0CON.0)
High level when
data > counter;
Low level when
data < counter
_
NOTE:
Interrupts are usually not used when timer 0 is configurared to operate in PWM mode
PND
Figure 10-4. Simplified Timer 0 Function Diagram: PWM Mode