Rainbow Electronics AT89LP216 - Manual (Page 33)

33
3621A–MICRO–6/06
AT89LP216 [Preliminary]
14.5.1 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 14-6 ). 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 14-6. Timer/Counter 1 PWM Mode 0
14.5.2 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 14-7 ).
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 frequency and duty cycle for Timer 0 in PWM Mode 1. Timer 1 in PWM Mode 1 is identi-
cal to Timer 0.
Mode 0:
f
out
Oscillator Frequency
256 2
PSC 0 1 + ×
-------------------------------------------------------
1
TPS
1 +
-------------------- ×
=
Mode 0: Duty Cycle % 100
RH0
256
------------ ×
=
OSC
TR1
GATE
INT1 Pin
TL1
(8 Bits)
Control
PSC1
TH1
(8 Bits)
OCR1
RH1
(8 Bits)
=
T1
÷TPS
Mode 1: f
out
Oscillator Frequency
256 256 RL 0 –
( ) ×
-------------------------------------------------------
1
TPS 1 +
-------------------- ×
=
Mode 1: Duty Cycle % 100
RH0
256
------------ Ч
=