PIC16F785-ESLASHSS datasheet(73/184 Pages) MICROCHIP

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Preliminary

DS41249B-page 71

PIC16F785

10.0

VOLTAGE REFERENCES

There are two voltage references available in the

PIC16F785: The voltage referred to as the comparator

reference (CVREF) is a variable voltage based on VDD;

The voltage referred to as the VR reference (VR) is a

fixed voltage derived from a stable band gap source.

Each source may be individually routed internally to the

comparators or output, buffered or unbuffered, on the

RA1/AN1/C12IN0-/VREF/ICSPCLK pin.

10.1

Comparator Reference

The comparator module also allows the selection of an

internally generated voltage reference for one of the

comparator inputs. The VRCON register

(Register 10-1) controls the voltage reference module

shown in Figure 10-1.

10.1.1

CONFIGURING THE VOLTAGE

REFERENCE

The voltage reference can output 32 distinct voltage

levels, 16 in a high range and 16 in a low range.

The following equation determines the output voltages:

EQUATION 10-1:

CVREF OUTPUT VOLTAGE

10.1.2

VOLTAGE REFERENCE

ACCURACY/ERROR

The full range of VSS to VDD cannot be realized due to

the construction of the module. The transistors on the

top and bottom of the resistor ladder network

(Figure 10-1) keep CVREF from approaching VSS or

VDD. The exception is when the module is disabled by

clearing all CVROE, C1VREN and C2VREN bits. When

disabled, the reference voltage is VSS when VR<3:0>

is ‘0000’ and the VRR (VRCON<5>) bit is set. This

allows the comparators to detect a zero-crossing and

not consume CVREF module current.

The voltage reference is VDD derived and therefore, the

CVREF output changes with fluctuations in VDD. The

tested absolute accuracy of the comparator voltage

reference can be found in Table 18-8.

FIGURE 10-1:

COMPARATOR VOLTAGE REFERENCE BLOCK DIAGRAM

VRR = 1 (low range):

CVREF = VR<3:0> X VDD/24

VRR = 0 (high range):

CVREF = (VDD/4) + (VR<3:0> X VDD/32)

VRR

VR3:VR0

16-1 Analog

C1VREF to

16 Stages

Comparator 1

Input

CVREN(1)

VDD

MUX

C2VREF to

Comparator 2

Input

1.2 V

C2VREN

C1VREN

CVREF

CVROE

Note

1: See Register 10-1, bits 3-0.

PIC16F785-E/SS Datasheet(PDF) 73 Page - Microchip Technology

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