PIC16LF1824 datasheet(220/440 Pages) MICROCHIP

220 / 440 page

PIC16(L)F1847

DS40001453D-page 220

Preliminary

 2011-2013 Microchip Technology Inc.

24.4.3

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

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

event may be generated by:

•A logic ‘0’ on the FLT0 pin

•A logic ‘1’ on a Comparator (Cx) output

A shutdown condition is indicated by the CCPxASE

(Auto-Shutdown Event Status) bit of the CCPxAS

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

shutdown state.

When a shutdown event occurs, two things happen:

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

remain set until cleared in firmware or an auto-restart

occurs (see Section 24.4.4 “Auto-restart Mode”).

The enabled PWM pins are asynchronously placed in

their shutdown states. The PWM output pins are

grouped into pairs [PxA/PxC] and [PxB/PxD]. The state

of each pin pair is determined by the PSSxAC and

PSSxBD bits of the CCPxAS register. Each pin pair may

be placed into one of three states:

•Drive logic ‘1’

•Drive logic ‘0’

• Tri-state (high-impedance)

FIGURE 24-14:

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

Note 1: The

auto-shutdown

condition

level-based signal, not an edge-based

signal. As long as the level is present, the

auto-shutdown will persist.

2: Writing to the CCPxASE bit of the

CCPxAS register is disabled while an

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.

4: Prior to an auto-shutdown event caused

by a comparator output or FLT0 pin event,

a software shutdown can be triggered in

firmware by setting the CCPxASE bit of

the CCPxAS register to ‘1’. The

Auto-Restart feature tracks the active

status of a shutdown caused by a

comparator output or FLT0 pin event only.

If it is enabled at this time, it will

immediately clear this bit and restart the

ECCP module at the beginning of the

next PWM period.

Shutdown

PWM

CCPxASE bit

Activity

Event

Shutdown

Event Occurs

Shutdown

Event Clears

PWM

Resumes

PWM Period

Start of

PWM Period

CCPxASE

Cleared by

Firmware

Timer

Overflow

Timer

Overflow

Timer

Overflow

Timer

Overflow

Missing Pulse

(Auto-Shutdown)

Missing Pulse

(CCPxASE not clear)

Timer

Overflow

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