PIC16F785T-ESLASHML datasheet(72/206 Pages) MICROCHIP

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PIC16F785/HV785

DS41249E-page 70

10.0

VOLTAGE REFERENCES

There are two voltage references available in the

PIC16F785/HV785: The voltage referred to as the

comparator reference (CVREF) is a variable voltage

based on VDD; The voltage referred to as the VR refer-

ence (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 with VR<3:0> = 0000 and VRR = 1 the refer-

ence voltage will be VSS. 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 19-8.

VRR = 1 (low range):

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

VRR = 0 (high range):

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

PIC16F785T-E/ML Datasheet(PDF) 72 Page - Microchip Technology

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