Specifications
57
3706C–MICRO–2/11
AT89LP3240/6440
11.5.1 Mode 0 – 8-bit PWM with 8-bit Logarithmic Prescaler
In Mode 0, TLx acts as a logarithmic prescaler driving 8-bit counter THx (see Figure 11-6). The
PSCx bits in TCONB control the prescaler value. On THx overflow, the duty cycle value in RHx
is transferred to OCRx and the output pin is set high. When the count in THx matches OCRx, the
output pin is cleared low. The following formulas give the output frequency and duty cycle for
Timer 0 in PWM Mode 0. Timer 1 in PWM Mode 0 is identical to Timer 0.
Figure 11-6.
Timer/Counter 1 PWM Mode 0
11.5.2 Mode 1 – 8-bit PWM with 8-bit Linear Prescaler
In Mode 1, TLx provides linear prescaling with an 8-bit auto-reload from RLx (see Figure 11-7 on
page 58). On TLx overflow, TLx is loaded with the value of RLx. THx acts as an 8-bit counter. On
THx overflow, the duty cycle value in RHx is transferred to OCRx and the output pin is set high.
When the count in THx matches OCRx, the output pin is cleared low. The following formulas
give the output freq
uency and duty cycle for Timer 0 in PWM Mode 1. Timer 1 in PWM Mode 1 is
identical to Timer 0.
11.5.3 Mode 2 – 8-bit Frequency Generator
Timer 0 in PWM Mode 2 functions as an 8-bit Auto-Reload timer, the same as normal Mode 2,
with the exception that the output pin T0 is toggled at every TL0 overflow (see Figure 11-8 and
Figure 11-9 on page 58). Timer 1 in PWM Mode 2 is identical to Timer 0. PWM Mode 2 can be
used to output a square wave of varying frequency. THx acts as an 8-bit counter. The following
formula gives the output frequency for Timer 0 in PWM Mode 2.
Mode 0:
f
out
Oscillator Frequency
256 2
PSC0 1+
×
-------------------------------------------------------
1
TPS 1+
---------------------
×=
Duty Cycle % 100
RH0
256
------------
×=
OSC
TR1
GATE1
INT1 Pin
TL1
(8 Bits)
Control
PSC1
TH1
(8 Bits)
OCR1
RH1
(8 Bits)
=
T1
÷TPS
Mode 1:
f
out
Oscillator Frequency
256 256 RL0–()×
-------------------------------------------------------
1
TPS 1+
---------------------
×=
Duty Cycle % 100
RH0
256
------------
×=
Mode 2: f
out
Oscillator Frequency
2256TH0–()×
-------------------------------------------------------
1
TPS 1+
---------------------
×=