STR720 datasheet(320/401 Pages) STMICROELECTRONICS

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STR720 - EXTENDED FUNCTION TIMER (EFT)

320/401

21.3.7

Pulse Width Modulation Mode

Pulse Width Modulation mode enables the generation of a signal with a frequency and pulse

length determined by the value of the OCAR and OCBR registers.

The pulse width modulation mode uses the complete Output Compare A function plus the

OCBR register.

21.3.7.1 Procedure

To use pulse width modulation mode select the following in the CR1 register:

– Using the OLVLA bit, select the level to be applied to the OCMPA pin after a successful com-

parison with OCAR register.

– Using the OLVLB bit, select the level to be applied to the OCMPA pin after a successful com-

parison with OCBR register.

– Set OCAE bit: the OCMPA pin is then dedicated to the output compare A function.

– Set the PWM bit.

– Select the timer clock (ECKGEN) and the prescaler division factor (CC7-CC0).

Load the OCBR register with the value corresponding to the period of the signal.

Load the OCAR register with the value corresponding to the length of the pulse if (OLVLA=0

and OLVLB=1).

Figure 52. One Pulse Mode Timing

COUNTER

....

FFFC FFFD FFFE

2ED0

2ED1 2ED2

2ED3

FFFC FFFD

OLVLB

OLVLA

ICAPA

OCMPA

compare A

Note: IEDGA=1, OCAR=2ED0h, OLVLA=0, OLVLB=1

COUNTER

....

FFFC FFFD FFFE

2ED0

2ED1 2ED2

2ED3

FFFC FFFD

OLVLB

OLVLA

ICAPA

OCMPA

compare A

Note: IEDGA=1, OCAR=2ED0h, OLVLA=0, OLVLB=1

0010

FFFC

4 clock period

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