Datasheet

PIC16F527
DS41652A-page 64 Preliminary  2012 Microchip Technology Inc.
10.1 Comparator Operation
A single comparator is shown in Figure 10-2 along with
the relationship between the analog input levels and
the digital output. When the analog input at V
IN+ is less
than the analog input V
IN-, the output of the comparator
is a digital low level. The shaded area of the output of
the comparator in Figure 10-2 represent the
uncertainty due to input offsets and response time. See
Table 15-2 for Common Mode Voltage.
FIGURE 10-2: SINGLE COMPARATOR
10.2 Comparator Reference
An internal reference signal may be used depending on
the comparator operating mode. The analog signal that
is present at V
IN- is compared to the signal at VIN+, and
the digital output of the comparator is adjusted
accordingly (Figure 10-2). Please see Section 11.0
“Comparator Voltage Reference Module” for internal
reference specifications.
10.3 Comparator Response Time
Response time is the minimum time after selecting a
new reference voltage or input source before the
comparator output is to have a valid level. If the
comparator inputs are changed, a delay must be used
to allow the comparator to settle to its new state. Please
see Table 15-6 for comparator response time
specifications.
10.4 Comparator Output
The comparator output is read through the CxOUT bit
in the CM1CON0 or CM2CON0 register. This bit is
read-only. The comparator output may also be used
externally, see Section 10.1 “Comparator Opera-
tion”.
10.5 Comparator Wake-up Flag
The Comparator Wake-up Flag bit, CWIF, in the
INTCON0 register, is set whenever all of the following
conditions are met:
•C1WU
= 0 (CM1CON0<0>) or
C2WU
= 0 (CM2CON0<0>)
• CM1CON0 or CM2CON0 has been read to latch
the last known state of the C1OUT and C2OUT bit
(MOVF CM1CON0, W)
• The output of a comparator has changed state
The wake-up flag may be cleared in software or by
another device Reset.
10.6 Comparator Operation During
Sleep
When the comparator is enabled it is active. To
minimize power consumption while in Sleep mode, turn
off the comparator before entering Sleep.
10.7 Effects of Reset
A Power-on Reset (POR) forces the CMxCON0
register to its Reset state. This forces the Comparator
input pins to analog Reset mode. Device current is
minimized when analog inputs are present at Reset
time.
10.8 Analog Input Connection
Considerations
A simplified circuit for an analog input is shown in
Figure 10-3. Since the analog pins are connected to a
digital output, they have reverse biased diodes to V
DD
and VSS. The analog input, therefore, must be between
V
SS and VDD. 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 may occur. A
maximum source impedance of 10 k is
recommended for the analog sources. Any external
component connected to an analog input pin, such as
a capacitor or a Zener diode, should have very little
leakage current.
–
+
VIN+
V
IN-
Result
Result
VIN-
VIN+
Note: Analog levels on any pin that is defined as
a digital input may cause the input buffer
to consume more current than is speci-
fied.