PIC16F-ESLASHML datasheet(69/178 Pages) MICROCHIP

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DS40044F-page 67

PIC16F627A/628A/648A

11.0

VOLTAGE REFERENCE

MODULE

The Voltage Reference module consists of a 16-tap

resistor ladder network that provides a selectable volt-

age reference. The resistor ladder is segmented to pro-

vide two ranges of VREF values and has a power-down

function to conserve power when the reference is not

being used. The VRCON register controls the opera-

tion 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 module can output 16 distinct

voltage levels for each range.

The equations used to calculate the output of the

Voltage Reference module are as follows:

if VRR = 1:

if VRR = 0:

The setting time of the Voltage Reference module must

be considered when changing the VREF output

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

reference is configured for an output voltage of 1.25V

with VDD = 5.0V.

VRCON – VOLTAGE REFERENCE CONTROL REGISTER (ADDRESS: 9Fh)

VREF

VR<3:0>

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

VDD

VREF

VDD

---

⎝⎠

⎛⎞

VR<3:0>

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

+VDD

R/W-0

U-0

R/W-0

VREN

VROE

VRR

—

VR3

VR2

VR1

VR0

bit 7

bit 0

bit 7

VREN: VREF Enable bit

= VREF circuit powered on

= VREF circuit powered down, no IDD drain

bit 6

VROE: VREF Output Enable bit

= VREF is output on RA2 pin

= VREF is disconnected from RA2 pin

bit 5

VRR: VREF Range Selection bit

= Low range

= High range

bit 4

Unimplemented: Read as ‘0’

bit 3-0

VR<3:0>: VREF Value Selection bits 0

≤ VR <3:0> ≤ 15

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

When VRR = 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

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