ADuC841 PWM: setting duty cycle to zero

Hello everybody,

I'm new to the ADuC841, my prior experience is with Cortex-M based microcontrollers.

I'm using ADuC841 with the dual 8-bit PWM mode on pins P3.4 and P3.3 (configured in sfr CFG841). 

For a simple 50% duty cycle with full 8-bit resolution I use this code:

PWM1L = 100; // output resolution PWM0
PWM1H = 100; // output resolutionPWM1

PWM0L = 50; // dutycycle PWM0

PWM0H = 50; // dutycycle PWM1

PWMCON = 0x53; // PWM on, Mode 5, Clk/1, Clk = Fosc

This results in a nice square wave with frequency = f_xtal / 100  and just about 50% duty cycle, see screenshot:

However, when I set duty cycle to 0%, there's still a small pulse output on the pins, see screenshot:

Instead I expect the PWM pins to stay permanently at low level.

Please advise how to set PWM output to 0% duty cycle.


Best regards,