Philips 8-bit microcontroller with two-clock 80C51 core UM10109 Manual De Usuario

 

© Koninklijke Philips Electronics N.V. 2005. All rights reserved.

PWM Operation has two main modes, asymmetrical and symmetrical. These modes of 
timer operation are selected by writing 10H or 11H to TMOD21:TMOD20 as shown in 

In asymmetrical PWM operation, the CCU Timer operates in downcounting mode 
regardless of the setting of TDIR2. In this case, TDIR2 will always read 1.

In symmetrical mode, the timer counts up/down alternately and the value of TDIR2 has no 
effect. The main difference from basic timer operation is the operation of the compare 
module, which in PWM mode is used for PWM waveform generation. 

 shows the 

behavior of the compare pins in PWM mode.

The user will have to configure the output compare pins as outputs in order to enable the 
PWM output. As with basic timer operation, when the PWM (compare) pins are connected 
to the compare logic, their logic state remains unchanged. However, since the bit FCO is 
used to hold the halt value, only a compare event can change the state of the pin.

The CCU Timer Overflow interrupt flag is set when the counter changes direction at the 
top. For example, if TOR contains 01FFH, CCU Timer will count: …01FEH, 01FFH, 
01FEH,… The flag is set in the counter cycle after the change from TOR to TOR-1. 

TOR2

compare value

timer value

non-inverted

inverted

0x0000

002aaa893

TOR2

compare value

timer value

non-inverted

inverted

002aaa894

0