PIC16F628A-ISLASHP datasheet(69/168 Pages) MICROCHIP

69 / 168 page

 2002 Microchip Technology Inc.

Preliminary

DS40044A-page 67

PIC16F627A/628A/648A

11.0 VOLTAGE REFERENCE

MODULE

The Voltage Reference is a 16-tap resistor ladder

network that provides a selectable voltage reference.

The resistor ladder is segmented to provide two ranges

of V

REF values and has a power-down function to

conserve power when the reference is not being used.

The VRCON register controls the operation of the

reference as shown in Figure 11-1. The block diagram

is given in Figure 11-1.

11.1

Voltage Reference Configuration

The Voltage Reference can output 16 distinct voltage

levels for each range.

The equations used to calculate the output of the

Voltage Reference are as follows:

if V

RR = 1:

if V

RR = 0:

The setting time of the Voltage Reference must be

considered when changing the V

REF output

(Table 17-3). Example 11-1 demonstrates how Voltage

Reference is configured for an output voltage of 1.25V

with V

DD = 5.0V.

VRCON REGISTER (ADDRESS: 9Fh)

FIGURE 11-1:

VOLTAGE REFERENCE BLOCK DIAGRAM

REF

R<3:0>

----------------------

REF

---



 VR<3:0>

----------------------

R/W-0

U-0

R/W-0

REN

ROE

—V

R3VR2VR1VR0

bit 7

bit 0

bit 7

REN: VREF Enable

1 = VREF circuit powered on

0 = VREF circuit powered down, no IDD drain

bit 6

ROE: VREF Output Enable

1 = VREF is output on RA2 pin

0 = VREF is disconnected from RA2 pin

bit 5

RR: VREF Range selection

1 = Low Range

0 = High Range

bit 4

Unimplemented: Read as '0'

bit 3-0

R<3:0>: VREF value selection 0

≤ VR [3:0] ≤ 15

When V

RR = 1: VREF = (VR<3:0>/ 24) * VDD

When V

RR = 0: VREF = 1/4 * VDD + (VR<3:0>/ 32) * VDD

Legend:

R = Readable bit

W = Writable bit

U = Unimplemented bit, read as ‘0’

-n = Value at POR

’1’ = Bit is set

’0’ = Bit is cleared

x = Bit is unknown

Note:

R is defined in Table 17-3.

VRR

VR3

VR0

(From VRCON<3:0>)

16-1 Analog Mux

VREN

VREF

16 Stages

VDD

VSS

PIC16F628A-I/P Datasheet(PDF) 69 Page - Microchip Technology

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