PIC18F2480/2580/4480/4580
FIGURE 21-3:
COMPARATOR OUTPUT BLOCK DIAGRAM
Port Pins
To RE1 or
RE2 Pin
D
Q
Bus
Data
CxINV
EN
Read CMCON
D
Q
Set
CMIF
bit
EN
CL
From
other
Comparator
Reset
21.6 Comparator Interrupts
21.7 Comparator Operation
During Sleep
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.
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.
While the comparator is powered up, higher Sleep
currents than shown in the power-down current
specification will occur. Each operational comparator
will consume additional current, as shown in the com-
parator 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.
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.
21.8 Effects of a Reset
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 (PIR
registers) interrupt flag may not get set.
A device Reset forces the CMCON register to its Reset
state, causing the comparator module to be in the Com-
parator Reset mode (CM<2:0> = 000). This ensures
that all potential inputs are analog inputs. Device
current is minimized when analog inputs are present at
Reset time. The comparators are powered down during
the Reset interval.
The user, in the Interrupt Service Routine, can clear the
interrupt in the following manner:
a) Any read or write of CMCON will end the
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.
DS39637D-page 266
© 2009 Microchip Technology Inc.
MICROCHIP [ MICROCHIP ]
