Datasheet

 2011-2012 Microchip Technology Inc. DS41441C-page 191
PIC12(L)F1840
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 FLT0 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
register. If the bit is a ‘0’, the PWM pins are operating
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 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.
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