AT89LP51RB2 datasheet(84/254 Pages) ATMEL

84 / 254 page

3722A–MICRO–10/11

AT89LP51RB2/RC2/IC2 Preliminary

13.6.1

Mode 0 – 8-bit PWM with 8-bit Logarithmic Prescaler

In Mode 0, TLn acts as a logarithmic prescaler driving 8-bit counter THn (see Figure 13-6). The

PSCn bits in TCONB control the prescaler value. On THn overflow, the duty cycle value in RHn

is transferred to OCRn and the output pin is set high. When the count in THn matches OCRn,

the output pin is cleared low. The following formulas give the output frequency and duty cycle for

Timer n in PWM Mode 0. Timer 1 in PWM Mode 0 is identical to Timer 0.

Note:

In Fast Mode, TPS applies only when the TnX2 bits in CKCON0 are set. TPS always

applies in Compatibility Mode, therefore setting TnX2 in Compatibility Mode will halve

the output frequency.

Figure 13-6. Timer/Counter 1 PWM Mode 0

13.6.2

Mode 1 – 8-bit PWM with 8-bit Linear Prescaler

In Mode 1, TLn provides linear prescaling with an 8-bit auto-reload from RLn (see Figure 13-7 on

page 85). On TLn overflow, TLn is loaded with the value of RLn. THn acts as an 8-bit counter.

On THn overflow, the duty cycle value in RHn is transferred to OCRn and the output pin is set

high. When the count in THn matches OCRn, the output pin is cleared low. The following formu-

las give the output frequency and duty cycle for Timer n in PWM Mode 1. Timer 1 in PWM Mode

1 is identical to Timer 0.

Note:

In Fast Mode, TPS applies only when the TnX2 bits in CKCON0 are set. TPS always

applies in Compatibility Mode, therefore setting TnX2 in Compatibility Mode will halve

the output frequency.

Mode 0:

out

SYS

256

PSCn

-----------------------------------------

TPS

---------------------

Duty Cycle %

100

RHn

256

------------

CLKSYS

TR1

GATE1

INT1 Pin

TL1

(8 Bits)

Control

PSC1

TH1

(8 Bits)

OCR1

RH1

(8 Bits)

÷TPS

Mode 1:

out

SYS

256

RLn

–

()

-------------------------------------------------

TPS

---------------------

Duty Cycle %

100

RHn

256

------------

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