41594B datasheet(199/372 Pages) MICROCHIP

199 / 372 page

 2011-2012 Microchip Technology Inc.

Preliminary

DS41594B-page 199

PIC12LF1840T48A

24.4.2

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 24.4.3 “Auto-Restart Mode”).

The enabled PWM pins are asynchronously placed in

their shutdown states. The PWM output pins are

grouped into pairs [P1A] and [P1B. 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)

FIGURE 24-10:

PWM AUTO-SHUTDOWN WITH FIRMWARE RESTART (P1RSEN = 0)

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.

Shutdown

PWM

CCP1ASE bit

Activity

Event

Shutdown

Event Occurs

Shutdown

Event Clears

PWM

Resumes

PWM Period

Start of

PWM Period

CCP1ASE

Cleared by

Firmware

Timer

Overflow

Timer

Overflow

Timer

Overflow

Timer

Overflow

Missing Pulse

(Auto-Shutdown)

Missing Pulse

(CCP1ASE not clear)

Timer

Overflow

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