PIC18F87K22 Datasheet, PDF(369/548 Page) Microchip Technology – 64/80-Pin, High-Performance, 1-Mbit Enhanced Flash Microcontrollers with 12-Bit A/D and nanoWatt XLP Technology

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PIC18F87K22 Datasheet, PDF (369/548 Pages) Microchip Technology – 64/80-Pin, High-Performance, 1-Mbit Enhanced Flash Microcontrollers with 12-Bit A/D and nanoWatt XLP Technology

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PIC18F87K22 FAMILY

24.5 Comparator Control and

Configuration

Each comparator has up to eight possible combina-

tions of inputs: up to four external analog inputs and

one of two internal voltage references.

All of the comparators allow a selection of the signal

from pin, CxINA, or the voltage from the comparator

reference (CVREF) on the non-inverting channel. This is

compared to either CxINB, CxINC, C2INB/C2IND or

the microcontrollerâs fixed internal reference voltage

(VBG, 1.024V nominal) on the inverting channel. The

comparator inputs and outputs are tied to fixed I/O pins,

defined in Table 24-1. The available comparator config-

urations and their corresponding bit settings are shown

in Figure 24-4.

TABLE 24-1: COMPARATOR INPUTS AND

OUTPUTS

Comparator Input or Output

I/O Pin

1

2

3

Note 1:

C1INA (VIN+)

RF6

C1INB (VIN-)

C1INC(1) (VIN-)

RF5

RH6

C2INB (VIN-)

RF3

C1OUT

RF2

C2INA (VIN+)

RF4

C2INB (VIN-)

C2INC(1) (VIN-)

C2IND(1) (VIN-)

RF3

RH4

RH5

C2OUT

RF1

C3INA (VIN+)

RG2

C3INB (VIN-)

RG3

C3INC (VIN-)

RG4

C2INB (VIN-)

RF3

C3OUT

RG1

C1INC, C2INC and C2IND are all

unavailable for 64-pin devices

(PIC18F6XK22).

24.5.1

COMPARATOR ENABLE AND

INPUT SELECTION

Setting the CON bit of the CMxCON register

(CMxCON<7>) enables the comparator for operation.

Clearing the CON bit disables the comparator, resulting

in minimum current consumption.

The CCH<1:0> bits in the CMxCON register

(CMxCON<1:0>) direct either one of three analog input

pins, or the Internal Reference Voltage (VBG), to the

comparator, VIN-. Depending on the comparator

operating mode, either an external or internal voltage

reference may be used. For external analog pins that

are unavailable in 64-pin devices (C1INC, C2INC and

C2IND), the corresponding configurations that use

them as inputs are unavailable.

The analog signal present at VIN- is compared to the

signal at VIN+ and the digital output of the comparator

is adjusted accordingly.

The external reference is used when CREF = 0

(CMxCON<2>) and VIN+ is connected to the CxINA

pin. When external voltage references are used, the

comparator module can be configured to have the

reference sources externally. The reference signal

must be between VSS and VDD and can be applied to

either pin of the comparator.

The comparator module also allows the selection of an

internally generated voltage reference (CVREF) from

the Comparator Voltage Reference module. This

module is described in more detail in Section 25.0

âComparator Voltage Reference Moduleâ. The

reference from the comparator voltage reference

module is only available when CREF = 1. In this mode,

the internal voltage reference is applied to the

comparatorâs VIN+ pin.

Note:

The comparator input pin selected by

CCH<1:0> must be configured as an input

by setting both the corresponding TRISF,

TRISG or TRISH bit and the corresponding

ANSELx bit in the ANCONx register.

24.5.2

COMPARATOR ENABLE AND

OUTPUT SELECTION

The comparator outputs are read through the CMSTAT

register. The CMSTAT<5> bit reads the Comparator 1

output, CMSTAT<6> reads Comparator 2 output and

CMSTAT<7> reads Comparator 3 output. These bits

are read-only.

The comparator outputs may also be directly output to

the RF2, RF1 and RG1 I/O pins by setting the COE bit

(CMxCON<6>). When enabled, multiplexers in the

output path of the pins switch to the output of the com-

parator. While in this mode, the TRISF<2:1> and

TRISG<1> bits still function as the digital output enable

bits for the RF2, RF1 and RG1 pins.

By default, the comparatorâs output is at logic high

whenever the voltage on VIN+ is greater than on VIN-.

The polarity of the comparator outputs can be inverted

using the CPOL bit (CMxCON<5>).

The uncertainty of each of the comparators is related to

the input offset voltage and the response time given in

the specifications, as discussed in Section 24.2

âComparator Operationâ.

ï£ 2010 Microchip Technology Inc.

Preliminary

DS39960B-page 369

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