Rainbow Electronics AT89LP214 - Manual (Page 35)

35
3538A–MICRO–7/06
AT89LP213/214 [Preliminary]
14.5.4 Mode 3 – Split 8-bit PWM
Timer 1 in PWM Mode 3 simply holds its count. The effect is the same as setting TR1 = 0.
Timer 0 in PWM Mode 3 establishes TL0 and TH0 as two separate PWM counters in a manner
similar to normal Mode 3. PWM Mode 3 on Timer 0 is shown in
Figure 14-9 . Only the Timer
Prescaler is available to change the output frequency during PWM Mode 3. TL0 can use the
Timer 0 control bits: GATE, TR0, INT0, PWM0EN and TF0. TH0 is locked into a timer function
and uses TR1, PWM1EN and TF1. RL0 provides the duty cycle for TL0 and RH0 provides the
duty cycle for TH0.
PWM Mode 3 is for applications requiring a single PWM channel and two timers, or two PWM
channels and an extra timer or counter. With Timer 0 in PWM Mode 3, the AT89LP213 can
appear to have three Timer/Counters. When Timer 0 is in PWM Mode 3, Timer 1 can be turned
on and off by switching it out of and into its own Mode 3. In this case, Timer 1 can still be used by
the serial port as a baud rate generator or in any application not requiring an interrupt. The fol-
lowing formulas give the output frequency and duty cycle for Timer 0 in PWM Mode 3.
Figure 14-9. Timer/Counter 0 PWM Mode 3
Mode 3:
f
out
Oscillator Frequency
256
-------------------------------------------------------
1
TPS
1 +
-------------------- ×
=
Mode 3, T0: Duty Cycle % 100
RL
0
256
----------- × =
Mode 3, T1: Duty Cycle % 100
RH 0
256
------------ ×
=
OSC
TR1
GATE
INT1 Pin
Control
TL0
(8 Bits)
OCR0
RL0
(8 Bits)
=
T0
OSC
TH0
(8 Bits)
OCR1
RH0
(8 Bits)
=
T1
TR1
÷TPS
÷TPS