PIC12F1822-ISLASHMF datasheet(215/398 Pages) MICROCHIP

215 / 398 page

 2010 Microchip Technology Inc.

Preliminary

DS41413A-page 215

PIC12F/LF1822/16F/LF1823

FIGURE 23-13:

EXAMPLE OF PWM DIRECTION CHANGE AT NEAR 100% DUTY CYCLE

23.4.3

ENHANCED PWM AUTO-

SHUTDOWN MODE

The PWM mode supports an Auto-Shutdown mode that

will disable the PWM outputs when an external

shutdown event occurs. Auto-Shutdown mode places

the PWM output pins into a predetermined state. This

mode is used to help prevent the PWM from damaging

the application.

The auto-shutdown sources are selected using the

CCP1AS<2:0> bits of the CCP1AS register. A shutdown

event may be generated by:

•A logic ‘0’ on the INT pin

• Comparator C1

• Setting the CCP1ASE bit in firmware

A shutdown condition is indicated by the CCP1ASE

(Auto-Shutdown Event Status) bit of the CCP1AS

normally. If the bit is a ‘1’, the PWM outputs are in the

shutdown state.

When a shutdown event occurs, two things happen:

The CCP1ASE bit is set to ‘1’. The CCP1ASE will

remain set until cleared in firmware or an auto-restart

occurs (see Section 23.4.4 “Auto-Restart Mode”).

The enabled PWM pins are asynchronously placed in

their shutdown states. The PWM output pins are

grouped into pairs [P1A/P1C] and [P1B/P1D]. The state

of each pin pair is determined by the PSS1AC and

PSS1BD bits of the CCP1AS register. Each pin pair may

be placed into one of three states:

• Drive logic ‘1’

• Drive logic ‘0’

• Tri-state (high-impedance)

Forward Period

Reverse Period

P1A

TON

TOFF

T = TOFF – TON

P1B

P1C

P1D

External Switch D

Potential

Shoot-Through Current

Note 1: All signals are shown as active-high.

2: TON is the turn-on delay of power switch QC and its driver.

3: TOFF is the turn-off delay of power switch QD and its driver.

External Switch C

Note 1: The auto-shutdown condition is a level-

based signal, not an edge-based signal.

As long as the level is present, the auto-

shutdown will persist.

2: Writing to the CCP1ASE bit is disabled

while

auto-shutdown

condition

persists.

3: Once the auto-shutdown condition has

been removed and the PWM restarted

(either through firmware or auto-restart)

the PWM signal will always restart at the

beginning of the next PWM period.

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