Microchip Technology DV164136 Data Sheet
PIC18F8722 FAMILY
DS39646C-page 284
© 2008 Microchip Technology Inc.
FIGURE 22-3:
COMPARATOR OUTPUT BLOCK DIAGRAM
22.6
Comparator Interrupts
The comparator interrupt flag is set whenever there is
a change in the output value of either comparator.
Software will need to maintain information about the
status of the output bits, as read from CMCON<7:6>, to
determine the actual change that occurred. The CMIF
bit (PIR2<6>) is the Comparator Interrupt Flag. The
CMIF bit must be reset by clearing it. Since it is also
possible to write a ‘1’ to this register, a simulated
interrupt may be initiated.
a change in the output value of either comparator.
Software will need to maintain information about the
status of the output bits, as read from CMCON<7:6>, to
determine the actual change that occurred. The CMIF
bit (PIR2<6>) is the Comparator Interrupt Flag. The
CMIF bit must be reset by clearing it. Since it is also
possible to write a ‘1’ to this register, a simulated
interrupt may be initiated.
Both the CMIE bit (PIE2<6>) and the PEIE bit
(INTCON<6>) must be set to enable the interrupt. In
addition, the GIE bit (INTCON<7>) must also be set. If
any of these bits are clear, the interrupt is not enabled,
though the CMIF bit will still be set if an interrupt
condition occurs.
(INTCON<6>) must be set to enable the interrupt. In
addition, the GIE bit (INTCON<7>) must also be set. If
any of these bits are clear, the interrupt is not enabled,
though the CMIF bit will still be set if an interrupt
condition occurs.
The user, in the Interrupt Service Routine, can clear the
interrupt in the following manner:
interrupt in the following manner:
a)
Any read or write of CMCON will end the
mismatch condition.
mismatch condition.
b)
Clear flag bit, CMIF.
A mismatch condition will continue to set flag bit, CMIF.
Reading CMCON will end the mismatch condition and
allow flag bit, CMIF, to be cleared.
Reading CMCON will end the mismatch condition and
allow flag bit, CMIF, to be cleared.
22.7
Comparator Operation
During Sleep
During Sleep
When a comparator is active and the device is placed
in Sleep mode, the comparator remains active and the
interrupt is functional if enabled. This interrupt will
wake-up the device from Sleep mode, when enabled.
Each operational comparator will consume additional
current, as shown in the comparator specifications. To
minimize power consumption while in Sleep mode, turn
off the comparators (CM<2:0> = 111) before entering
Sleep. If the device wakes up from Sleep, the contents
of the CMCON register are not affected.
in Sleep mode, the comparator remains active and the
interrupt is functional if enabled. This interrupt will
wake-up the device from Sleep mode, when enabled.
Each operational comparator will consume additional
current, as shown in the comparator specifications. To
minimize power consumption while in Sleep mode, turn
off the comparators (CM<2:0> = 111) before entering
Sleep. If the device wakes up from Sleep, the contents
of the CMCON register are not affected.
22.8
Effects of a Reset
A device Reset forces the CMCON register to its Reset
state, causing the comparator modules to be turned off
(CM<2:0> = 111). However, the input pins (RF3
through RF6) are configured as analog inputs by
default on device Reset. The I/O configuration for these
pins is also determined by the setting of the
PCFG<3:0> bits (ADCON1<3:0>). Therefore, device
current is minimized when analog inputs are present at
Reset time.
state, causing the comparator modules to be turned off
(CM<2:0> = 111). However, the input pins (RF3
through RF6) are configured as analog inputs by
default on device Reset. The I/O configuration for these
pins is also determined by the setting of the
PCFG<3:0> bits (ADCON1<3:0>). Therefore, device
current is minimized when analog inputs are present at
Reset time.
D
Q
EN
CxOUT
Bus
Data
Data
Set
MUL
T
IP
LE
X
CMIF
bit
bit
-+
Port pins
Read CMCON
Reset
From
Other
Comparator
CxINV
D
Q
EN
CL
Note:
If a change in the CMCON register
(C1OUT or C2OUT) should occur when a
read operation is being executed (start of
the Q2 cycle), then the CMIF (PIR2
register) interrupt flag may not get set.
(C1OUT or C2OUT) should occur when a
read operation is being executed (start of
the Q2 cycle), then the CMIF (PIR2
register) interrupt flag may not get set.