PIC18F45J10 FAMILY
19.3.2
INTERNAL REFERENCE SIGNAL
19.2 Comparator Operation
The comparator module also allows the selection of an
internally generated voltage reference from the
comparator voltage reference module. This module is
described in more detail in Section 20.0 “Comparator
Voltage Reference Module”.
A single comparator is shown in Figure 19-2, 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 19-2
represent the uncertainty due to input offsets and
response time.
The internal reference is only available in the mode
where four inputs are multiplexed to two comparators
(CM<2:0> = 110). In this mode, the internal voltage
reference is applied to the VIN+ pin of both comparators.
19.4 Comparator Response Time
19.3 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 ref-
erence is changed, the maximum delay of the internal
voltage reference must be considered when using the
comparator outputs. Otherwise, the maximum delay of
the comparators should be used (see Section 24.0
“Electrical Characteristics”).
Depending on the comparator operating mode, either
an external or internal voltage reference may be used.
The analog signal present at VIN- is compared to the
signal at VIN+ and the digital output of the comparator
is adjusted accordingly (Figure 19-2).
FIGURE 19-2:
SINGLE COMPARATOR
19.5 Comparator Outputs
VIN+
VIN-
+
The comparator outputs are read through the CMCON
register. These bits are read-only. The comparator
outputs may also be directly output to the RB5 and RA5
I/O pins. When enabled, multiplexors in the output path
of the RB5 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 19-3 shows the comparator output block
diagram.
Output
–
VIN-
VIN+
The TRISA bits will still function as an output enable/
disable for the RB5 and RA5 pins while in this mode.
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.
19.3.1
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.
© 2009 Microchip Technology Inc.
DS39682E-page 227
MICROCHIP [ MICROCHIP ]
