PIC16C717-I/SS View Datasheet(PDF) - Microchip Technology

Part Name

Description

Manufacturer

PIC16C717-I/SS

18/20-Pin, 8-Bit CMOS Microcontrollers with 10/12-Bit A/D

Microchip Technology 

PIC16C717/770/771

REGISTER 10-2: VOLTAGE REFERENCE CONTROL REGISTER (REFCON: 9BH)

R/W-0

R/W-0

R/W-0

R/W-0

U-0

U-0

U-0

U-0

VRHEN VRLEN VRHOEN VRLOEN

—

—

—

—

R = Readable bit

bit7

bit0 W = Writable bit

U = Unimplemented bit,

read as ‘0’

- n = Value at POR reset

bit 7: VRHEN: Voltage Reference High Enable bit (VRH = 4.096V nominal)

1 = Enabled, powers up reference generator

0 = Disabled, powers down reference generator if unused by LVD, BOR, or VRL

bit 6:

VRLEN: Voltage Reference Low Enable bit (VRL = 2.048V nominal)

1 = Enabled, powers up reference generator

0 = Disabled, powers down reference generator if unused by LVD, BOR, or VRH

bit 5:

VRHOEN: High Voltage Reference Output Enable bit

1 = Enabled, VRH analog reference is output on RA3 if enabled (VRHEN = 1)

0 = Disabled, analog reference is used internally only

bit 4:

VRLOEN: Low Voltage Reference Output Enable bit

1 = Enabled, VRL analog reference is output on RA2 if enabled (VRLEN = 1)

0 = Disabled, analog reference is used internally only

bit 3-0: Unimplemented: Read as '0’

10.1 Bandgap Voltage Reference

The bandgap module generates a stable voltage refer-

ence of over a range of temperatures and device supply

voltages. This module is enabled anytime any of the fol-

lowing are enabled:

• Brown-out Reset

• Low-voltage Detect

• Either of the internal analog references (VRH,

VRL)

Whenever the above are all disabled, the bandgap

module is disabled and draws no current.

10.2 Internal VREF for A/D Converter

The bandgap output voltage is used to generate two

stable references for the A/D converter module. These

references are enabled in software to provide the user

with the means to turn them on and off in order to min-

imize current consumption. Each reference can be indi-

vidually enabled.

The VRH reference is enabled with control bit VRHEN

(REFCON<7>). When this bit is set, the gain amplifier

is enabled. After a specified start-up time a stable ref-

erence of 4.096V nominal is generated and can be

used by the A/D converter as a reference input.

The VRL reference is enabled by setting control bit

VRLEN (REFCON<6>). When this bit is set, the gain

amplifier is enabled. After a specified start up time a

stable reference of 2.048V nominal is generated and

can be used by the A/D converter as a reference input.

Each voltage reference is available for external use via

VRL and VRH pins.

Each reference, if enabled, can be output on an exter-

nal pin by setting the VRHOEN (high reference output

enable) or VRLOEN (low reference output enable) con-

trol bit. If the reference is not enabled, the VRHOEN

and VRLOEN bits will have no effect on the corre-

sponding pin. The device specific pin can then be used

as general purpose I/O.

Note:

If VRH or VRL is enabled and the other ref-

erence (VRL or VRH), the BOR, and the

LVD modules are not enabled, the band-

gap will require a start-up time before the

bandgap reference is stable. Before using

the internal VRH or VRL reference, ensure

that the bandgap reference voltage is sta-

ble by monitoring the BGST bit in the LVD-

CON register. The voltage references will

not be reliable until the bandgap is stable

as shown by BGST being set.

DS41120A-page 110

Advanced Information

© 1999 Microchip Technology Inc.

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