PIC18F2220/2320/4220/4320
16.4.5.1
Auto-Shutdown and Automatic
Restart
16.4.6
START-UP CONSIDERATIONS
When the ECCP 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 exter-
nal 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 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
PWM1CON register (PWM1CON<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 firm-
ware. Once ECCPASE is cleared, the enhanced PWM
will resume at the beginning of the next PWM period.
The CCP1M1:CCP1M0 bits (CCP1CON<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 polar-
ities must be selected before the PWM pins are config-
ured 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.
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 shut-
down condition is a level. The ECCPASE bit cannot be
cleared as long as the cause of the shutdown persists.
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 ECCP module may cause damage to the application
circuit. The ECCP module must be enabled in the proper
output mode and complete a full PWM cycle before con-
figuring 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.
The Auto-Shutdown mode can be forced by writing a ‘1’
to the ECCPASE bit.
FIGURE 16-10:
PWM AUTO-SHUTDOWN (PRSEN = 1, AUTO-RESTART ENABLED)
PWM Period
PWM Period
PWM Period
PWM Activity
Dead Time
Duty Cycle
Dead Time
Duty Cycle
Dead Time
Duty Cycle
Shutdown Event
ECCPASE bit
FIGURE 16-11:
PWM AUTO-SHUTDOWN (PRSEN = 0, AUTO-RESTART DISABLED)
PWM Period
PWM Period
PWM Period
PWM Activity
Dead Time
Duty Cycle
Dead Time
Duty Cycle
Dead Time
Duty Cycle
Shutdown Event
ECCPASE bit
ECCPASE
Cleared by Firmware
2003 Microchip Technology Inc.
DS39599C-page 151
MICROCHIP [ MICROCHIP ]
