Datasheet

 2007-2012 Microchip Technology Inc. DS39778E-page 325
PIC18F87J11 FAMILY
23.6 Comparator Interrupts
The comparator interrupt flag is set whenever any of
the following occurs:
• Low-to-high transition of the comparator output
• High-to-low transition of the comparator output
• Any change in the comparator output
The comparator interrupt selection is done by the
EVPOL<1:0> bits in the CMxCON register
(CMxCON<4:3>).
In order to provide maximum flexibility, the output of the
comparator may be inverted using the CPOL bit in the
CMxCON register (CMxCON<5>). This is functionally
identical to reversing the inverting and non-inverting
inputs of the comparator for a particular mode.
An interrupt is generated on the low-to-high or high-to-
low transition of the comparator output. This mode of
interrupt generation is dependent on EVPOL<1:0> in
the CMxCON register. If EVPOL<1:0> = 01 or 10, the
interrupt is generated on a low-to-high or high-to-low
transition of the comparator output. Once the interrupt
is generated, it is required to clear the interrupt flag by
software.
When EVPOL<1:0> = 11, the comparator interrupt flag
is set whenever there is a change in the output value of
either comparator. Software will need to maintain infor-
mation about the status of the output bits, as read from
CMSTAT<1:0>, to determine the actual change that
occurred. The CMxIF bits (PIR2<6:5>) are the Compar-
ator Interrupt Flags. The CMxIF bits must be reset by
clearing them. Since it is also possible to write a ‘1’ to
this register, a simulated interrupt may be initiated.
Table 23-2 shows the interrupt generation with respect
to comparator input voltages and EVPOLx bit settings.
Both the CMxIE bits (PIE2<6:5>) 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 CMxIF bits will still be set if an interrupt
condition occurs.
TABLE 23-2: COMPARATOR INTERRUPT GENERATION
CPOL EVPOL<1:0>
Comparator
Input Change
CxOUT Transition
Interrupt
Generated
0
00
V
IN+ > VIN- Low-to-High No
VIN+ < VIN- High-to-Low No
01
V
IN+ > VIN- Low-to-High Yes
VIN+ < VIN- High-to-Low No
10
VIN+ > VIN- Low-to-High No
V
IN+ < VIN- High-to-Low Yes
11
VIN+ > VIN- Low-to-High Yes
VIN+ < VIN- High-to-Low Yes
1
00
V
IN+ > VIN- High-to-Low No
VIN+ < VIN- Low-to-High No
01
V
IN+ > VIN- High-to-Low No
V
IN+ < VIN- Low-to-High Yes
10
VIN+ > VIN- High-to-Low Yes
V
IN+ < VIN- Low-to-High No
11
V
IN+ > VIN- High-to-Low Yes
VIN+ < VIN- Low-to-High Yes