PIC18F258 MICROCHIP [Microchip Technology], PIC18F258 Datasheet - Page 249

• Manufacturer Part Number: PIC18F258
• Description: High Performance, 28/40-Pin Enhanced FLASH Microcontrollers with CAN
• Manufacturer: MICROCHIP [Microchip Technology]

21.2
A single comparator is shown in Figure 21-2 along with
the relationship between the analog input levels and
the digital output. When the analog input at V
than the analog input V
is a digital low level. When the analog input at V
greater than the analog input V
comparator is a digital high level. The shaded areas of
the output of the comparator in Figure 21-2 represent
the uncertainty due to input offsets and response time.
21.3
An external or internal reference signal may be used
depending on the Comparator Operating mode. The
analog signal present at V
at V
adjusted accordingly (Figure 21-2).
FIGURE 21-2:
21.3.1
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 V
pin of the comparator(s).
Output
V
V
2002 Microchip Technology Inc.
V
IN
IN
V
utput
IN
IN–
IN+
-
+
+, and the digital output of the comparator is
V
V
IN
IN
Comparator Operation
Comparator Reference
+
-
EXTERNAL REFERENCE SIGNAL
SS
and V
+
-
SINGLE COMPARATOR
DD
IN
-, the output of the comparator
, and can be applied to either
IN
- is compared to the signal
IN
-, the output of the
Output
IN
+ is less
IN
+ is
Preliminary
21.3.2
The comparator module also allows the selection of an
internally generated voltage reference for the compara-
tors. Section 22.0 contains a detailed description of the
Comparator Voltage Reference Module that provides
this signal. The internal reference signal is used when
comparators are in mode CM<2:0> = 110 (Figure 21-1).
In this mode, the internal voltage reference is applied to
the V
21.4
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 (Section 27.0).
21.5
The comparator outputs are read through the CMCON
register. These bits are read only. The comparator
outputs may also be directly output to the RE1 and RE2
I/O pins. When enabled, multiplexors in the output path
of the RE1 and RE2 pins will switch and the output of
each pin will be the unsynchronized output of the com-
parator. The uncertainty of each of the comparators is
related to the input offset voltage and the response time
given in the specifications. Figure 21-3 shows the
comparator output block diagram.
The TRISE bits will still function as an output enable/
disable for the RE1 and RE2 pins while in this mode.
The polarity of the comparator outputs can be changed
using the C2INV and C1INV bits (CMCON<4:5>).
Note 1: When reading the PORT register, all pins
IN
+ pin of both comparators.
Comparator Response Time
Comparator Outputs
2: Analog levels on any pin defined as a dig-
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.
INTERNAL REFERENCE SIGNAL
ital input, may cause the input buffer to
consume more current than is specified.
PIC18FXX8
DS41159B-page 247