2003 Microchip Technology Inc.
DS39582B-page 139
PIC16F87XA
12.7
Comparator Operation 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.
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.
12.8
Effects of a Reset
A device Reset forces the CMCON register to its Reset
state, causing the comparator module to be in the
Comparator Off mode, CM<2:0> =
111
. This ensures
compatibility to the PIC16F87X devices.
12.9
Analog Input Connection
Considerations
A simplified circuit for an analog input is shown in
Figure 12-4. Since the analog pins are connected to a
digital output, they have reverse biased diodes to V
DD
and V
SS
. The analog input, therefore, must be between
V
SS
and V
DD
. If the input voltage deviates from this
range by more than 0.6V in either direction, one of the
diodes is forward biased and a latch-up condition may
occur. A maximum source impedance of 10 k
Ω
is rec-
ommended for the analog sources. Any external com-
ponent connected to an analog input pin, such as a
capacitor or a Zener diode, should have very little
leakage current.
FIGURE 12-4:
ANALOG INPUT MODEL
VA
R
S
< 10K
A
IN
C
PIN
5 pF
V
DD
V
T
= 0.6 V
V
T
= 0.6 V
R
IC
I
LEAKAGE
±500 nA
V
SS
Legend:
C
PIN
= Input Capacitance
V
T
= Threshold
Voltage
I
LEAKAGE
= Leakage Current at the pin due to various junctions
R
IC
= Interconnect Resistance
R
S
= Source
Impedance
VA
= Analog
Voltage
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