PIC18F2682 Datasheet, PDF (186/484 Pages) Microchip Technology – 28/40/44-Pin Enhanced Flash Microcontrollers with ECAN Technology, 10-Bit A/D and nanoWatt Technology

PIC18F2682/2685/4682/4685
16.4.7.1 Auto-Shutdown and Auto-Restart
The auto-shutdown feature can be configured to allow
automatic restarts of the module following a shutdown
event. This is enabled by setting the PRSEN bit of the
ECCP1DEL register (ECCP1DEL<7>).
In Shutdown mode with PRSEN = 1 (Figure 16-10), the
ECCPASE bit will remain set for as long as the cause
of the shutdown continues. When the shutdown condi-
tion clears, the ECCPASE bit is cleared. If PRSEN = 0
(Figure 16-11), once a shutdown condition occurs, the
ECCPASE bit will remain set until it is cleared by
firmware. Once ECCPASE is cleared, the Enhanced
PWM will resume at the beginning of the next PWM
period.
Note: Writing to the ECCPASE bit is disabled
while a shutdown condition is active.
Independent of the PRSEN bit setting, if the auto-
shutdown source is one of the comparators, the
shutdown condition is a level. The ECCPASE bit
cannot be cleared as long as the cause of the shutdown
persists.
The Auto-Shutdown mode can be forced by writing a ‘1’
to the ECCPASE bit.
16.4.8 START-UP CONSIDERATIONS
When the ECCP1 module is used in the PWM mode, the
application hardware must use the proper external pull-up
and/or pull-down resistors on the PWM output pins. When
the microcontroller is released from Reset, all of the I/O
pins are in the high-impedance state. The external circuits
must keep the power switch devices in the OFF state until
the microcontroller drives the I/O pins with the proper
signal levels, or activates the PWM output(s).
The ECCP1M1:ECCP1M0 bits (ECCP1CON<1:0>)
allow the user to choose whether the PWM output
signals are active-high or active-low for each pair of
PWM output pins (P1A/P1C and P1B/P1D). The PWM
output polarities must be selected before the PWM pins
are configured as outputs. Changing the polarity
configuration while the PWM pins are configured as
outputs is not recommended, since it may result in
damage to the application circuits.
The P1A, P1B, P1C and P1D output latches may not be
in the proper states when the PWM module is initialized.
Enabling the PWM pins for output at the same time as
the ECCP1 module may cause damage to the applica-
tion circuit. The ECCP1 module must be enabled in the
proper output mode and complete a full PWM cycle
before configuring the PWM pins as outputs. The
completion of a full PWM cycle is indicated by the
TMR2IF bit being set as the second PWM period begins.
FIGURE 16-10: PWM AUTO-SHUTDOWN (PRSEN = 1, AUTO-RESTART ENABLED)
Shutdown Event
PWM Period
ECCPASE bit
PWM Activity
Start of
PWM Period
Normal PWM
Shutdown Shutdown
Event Occurs Event Clears
PWM
Resumes
FIGURE 16-11: PWM AUTO-SHUTDOWN (PRSEN = 0, AUTO-RESTART DISABLED)
Shutdown Event
PWM Period
ECCPASE bit
PWM Activity
Start of
PWM Period
Normal PWM
ECCPASE
Shutdown
Cleared by
Event Occurs _Shutdown ^Firmware _PWM
Event Clears
Resumes
DS39761B-page 184
Preliminary
© 2007 Microchip Technology Inc.