PIC18F67J11T-I Datasheet, PDF(323/466 Page) Microchip Technology – 64/80-Pin, High-Performance, 1-Mbit Flash Microcontrollers

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PIC18F67J11T-I Datasheet, PDF (323/466 Pages) Microchip Technology – 64/80-Pin, High-Performance, 1-Mbit Flash Microcontrollers

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PIC18F87J11 FAMILY

23.5 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.

Both comparators allow a selection of the signal from

pin, CxINA, or the voltage from the comparator refer-

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

compared to either CxINB, CxINC, CxIND or the micro-

controllerâs fixed internal reference voltage (VIRV, 1.2V

nominal) on the inverting channel. The comparator

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

Table 23-1. The available configurations and their

corresponding bit settings are shown in Figure 23-1.

TABLE 23-1: COMPARATOR INPUTS AND

OUTPUTS

Comparator Input or Output

I/O Pin

1

2

Note 1:

C1INA (VIN+)

RF6

C1INB (VIN-)

RF5

C1INC (VIN-)(1)

RH6(1)

C1OUT

RF2

C2INA(VIN+)

RF4

C2INB(VIN-)

RF3

C2INC(VIN-)(1)

RH4(1)

C2IND(VIN-)(1)

RH5(1)

C2OUT

RF1

Available in 80-pin devices only.

23.5.1

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 (VIRV), to the

comparator VIN-. Depending on the comparator operat-

ing 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.

The external reference is used when

CREF (CMxCON<2>) = 0 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 24.0 âCompara-

tor Voltage Reference Moduleâ. The reference from

the comparator voltage reference module is only avail-

able 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 or

TRISH bit, and the corresponding PCFGx

bit in the ANCON1 register.

23.5.1.1 Comparator Configurations in 64-Pin

and 80-Pin Devices

In PIC18F87J11 family devices, the C and D input chan-

nels for both comparators are linked to pins in PORTH

and cannot be reassigned to alternate analog inputs.

Because of this, 64-pin devices offer a total of 4 different

configurations for each comparator. In contrast, 80-pin

devices offer a choice of 6 configurations for

Comparator 1 and 8 configurations for Comparator 2.

The configurations shown in Figure 23-1 are footnoted to

indicate where they are not available.

23.5.2

COMPARATOR ENABLE AND

OUTPUT SELECTION

The comparator outputs are read through the CMSTAT

register. The CMSTAT<0> reads the Comparator 1 out-

put and CMSTAT<1> reads the Comparator 2 output.

These bits are read-only.

The comparator outputs may also be directly output to

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

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

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

parator. The TRISF<2:1> bits still function as the digital

output enable bits for the RF1 and RF2 pins while in

this mode.

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 23.2

âComparator Operationâ.

ï£ 2007-2012 Microchip Technology Inc.

DS39778E-page 323

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