PIC16F7X7
13.3.2
INTERNAL REFERENCE SIGNAL
13.2 Comparator Operation
The comparator module also allows the selection of an
internally generated voltage reference for the compar-
ators. Section 14.0 “Comparator Voltage Reference
Module” contains a detailed description of the com-
parator voltage reference module that provides this
signal. The internal reference signal is used when
comparators are in mode CM<2:0> = 110(Figure 13-1).
In this mode, the internal voltage reference is applied to
the VIN+ pin of both comparators.
A single comparator is shown in Figure 13-2, along with
the relationship between the analog input levels and
the digital output. When the analog input at VIN+ is less
than the analog input VIN-, the output of the comparator
is a digital low level. When the analog input at VIN+ is
greater than the analog input VIN-, the output of the
comparator is a digital high level. The shaded areas of
the output of the comparator in Figure 13-2 represent
the uncertainty due to input offsets and response time.
13.4 Comparator Response Time
13.3 Comparator Reference
Response time is the minimum time after selecting a
new reference voltage, or input source, before the
comparator output has a valid level. If the internal
reference is changed, the maximum delay of the inter-
nal voltage reference must be considered when using
the comparator outputs. Otherwise, the maximum
delay of the comparators should be used (Section 18.0
“Electrical Characteristics”).
An external or internal reference signal may be used
depending on the comparator operating mode. The
analog signal present at VIN- is compared to the signal
at VIN+ and the digital output of the comparator is
adjusted accordingly (Figure 13-2).
FIGURE 13-2:
SINGLE COMPARATOR
13.5 Comparator Outputs
VIN+
VIN-
+
Output
The comparator outputs are read through the CMCON
register. These bits are read-only. The comparator
outputs may also be directly output to the RA4 and RA5
I/O pins. When enabled, multiplexors in the output path
of the RA4 and RA5 pins will switch and the output of
each pin will be the unsynchronized output of the
comparator. The uncertainty of each of the
comparators is related to the input offset voltage and
the response time given in the specifications.
Figure 13-3 shows the comparator output block
diagram.
–
VIN-
V
IN–
VIN+
V
IN+
The TRISA bits will still function as an output enable/
disable for the RA4 and RA5 pins while in this mode.
Output
Output
The polarity of the comparator outputs can be changed
using the C2INV and C1INV bits (CMCON<5:4:>).
Note 1: When reading the Port register, all pins
configured as analog inputs will read as a
‘0’. Pins configured as digital inputs will
convert an analog input according to the
Schmitt Trigger input specification.
13.3.1
EXTERNAL REFERENCE SIGNAL
When external voltage references are used, the
comparator module can be configured to have the com-
parators operate from the same or different reference
sources. However, threshold detector applications may
require the same reference. The reference signal must
be between VSS and VDD and can be applied to either
pin of the comparator(s).
2: Analog levels on any pin defined as a
digital input may cause the input buffer to
consume more current than is specified.
3: RA4 is an open collector I/O pin. When
used as an output, a pull-up resistor is
required.
2004 Microchip Technology Inc.
DS30498C-page 163
MICROCHIP [ MICROCHIP ]
