ST72561J4-Auto datasheet(116/324 Pages) STMICROELECTRONICS

116 / 324 page

16-bit timer

ST72561-Auto

116/324

Doc ID 12370 Rev 8

Procedure

To use Pulse Width Modulation mode:

Load the OC2R register with the value corresponding to the period of the signal using

the formula in the opposite column.

Load the OC1R register with the value corresponding to the period of the pulse if

(OLVL1 = 0 and OLVL2 = 1) using the formula in the opposite column.

Select the following in the CR1 register:

–

Using the OLVL1 bit, select the level to be applied to the OCMP1 pin after a

successful comparison with the OC1R register.

–

Using the OLVL2 bit, select the level to be applied to the OCMP1 pin after a

successful comparison with the OC2R register.

Select the following in the CR2 register:

–

Set OC1E bit: the OCMP1 pin is then dedicated to the output compare 1 function.

–

Set the PWM bit.

–

Select the timer clock (CC[1:0]) (see Table 50).

If OLVL1 = 1 and OLVL2 = 0 the length of the positive pulse is the difference between the

OC2R and OC1R registers.

If OLVL1 = OLVL2 a continuous signal will be seen on the OCMP1 pin.

The OCiR register value required for a specific timing application can be calculated using

the following formula:

Where:

= Signal or pulse period (in seconds)

fCPU

CPU clock frequency (in hertz)

PRESC =

Timer prescaler factor (2, 4 or 8 depending on CC[1:0] bits, see Table 50)

If the timer clock is an external clock the formula is:

Where:

Signal or pulse period (in seconds)

Counter

OCMP1 = OLVL2

Counter

= OC2R

OCMP1 = OLVL1

When

= OC1R

Pulse Width Modulation cycle

Counter is reset

to FFFCh

ICF1 bit is set

OCiR Value =

t * fCPU

PRESC

- 5

OCiR =

t * fEXT -5

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