PIC18F45K80-I Datasheet, PDF (278/622 Pages) Microchip Technology – 28/40/44/64-Pin, Enhanced Flash Microcontrollers with ECAN and nanoWatt XLP Technology

PIC18F66K80 FAMILY
FIGURE 20-11:
EXAMPLE OF PWM DIRECTION CHANGE AT NEAR 100% DUTY CYCLE
Forward Period
t1
Reverse Period
P1A
P1B
P1C
P1D
PW
External Switch C
External Switch D
Potential
Shoot-Through Current
PW
TON
TOFF
T = TOFF – TON
Note 1:
2:
3:
All signals are shown as active-high.
TON is the turn-on delay of power switch, QC, and its driver.
TOFF is the turn-off delay of power switch, QD, and its driver.
20.4.3 START-UP CONSIDERATIONS
When any PWM mode is used, the application
hardware must use the proper external pull-up and/or
pull-down resistors on the PWM output pins.
Note:
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 micro-
controller drives the I/O pins with the
proper signal levels or activates the PWM
output(s).
The CCP1M<1:0> bits of the CCP1CON register 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 pin output
drivers are enabled. Changing the polarity configura-
tion while the PWM pin output drivers are enabled 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 pin output drivers at the
same time as the Enhanced PWM modes may cause
damage to the application circuit. The Enhanced PWM
modes must be enabled in the proper Output mode and
complete a full PWM cycle before enabling the PWM
pin output drivers. The completion of a full PWM cycle
is indicated by the TMR2IF or TMR4IF bit of the PIR1
or PIR4 register being set as the second PWM period
begins.
20.4.4
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
ECCP1AS<2:0> bits (ECCP1AS<6:4>). A shutdown
event may be generated by:
• A logic ‘0’ on the pin that is assigned the FLT0
input function
• Comparator C1
• Comparator C2
• Setting the ECCP1ASE bit in firmware
DS39977F-page 278
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