PIC16LC620-04SLASHP datasheet(44/108 Pages) MICROCHIP

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PIC16C62X

DS30235G-page 44

Preliminary

EXAMPLE 8-1:

VOLTAGE REFERENCE

CONFIGURATION

8.2

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 8-2) keep VREF from approaching VSS or VDD.

The Voltage Reference is VDD derived and therefore,

the VREF output changes with ﬂuctuations in VDD. The

tested absolute accuracy of the Voltage Reference can

be found in Table 12-3.

8.3

Operation During Sleep

When the device wakes up from sleep through an

interrupt or a Watchdog Timer time-out, the contents of

the VRCON register are not affected. To minimize

current consumption in SLEEP mode, the Voltage

Reference should be disabled.

MOVLW

0x02

; 4 Inputs Muxed

MOVWF

CMCON

; to 2 comps.

BSF

STATUS,RP0

; go to Bank 1

MOVLW

0x07

; RA3-RA0 are

MOVWF

TRISA

; outputs

MOVLW

0xA6

; enable VREF

MOVWF

VRCON

; low range

; set VR<3:0>=6

BCF

STATUS,RP0

; go to Bank 0

CALL

DELAY10

; 10

µs delay

8.4

Effects of a Reset

A device reset disables the Voltage Reference by clear-

ing bit VREN (VRCON<7>). This reset also disconnects

the reference from the RA2 pin by clearing bit VROE

(VRCON<6>) and selects the high voltage range by

clearing bit VRR (VRCON<5>). The VREF value select

bits, VRCON<3:0>, are also cleared.

8.5

Connection Considerations

The Voltage Reference Module operates independently

of the comparator module. The output of the reference

generator may be connected to the RA2 pin if the

TRISA<2> bit is set and the VROE bit, VRCON<6>, is

set. Enabling the Voltage Reference output onto the

RA2 pin with an input signal present will increase cur-

rent consumption. Connecting RA2 as a digital output

with VREF enabled will also increase current consump-

tion.

The RA2 pin can be used as a simple D/A output with

limited drive capability. Due to the limited drive

capability, a buffer must be used in conjunction with the

Voltage Reference output for external connections to

VREF.

Figure 8-3

shows

example

buffering

technique.

FIGURE 8-3:

VOLTAGE REFERENCE OUTPUT BUFFER EXAMPLE

TABLE 8-1:

REGISTERS ASSOCIATED WITH VOLTAGE REFERENCE

Note:

- = Unimplemented, read as "0"

Address

Name

Bit 7

Bit 6

Bit 5

Bit 4

Bit 3

Bit 2

Bit 1

Bit 0

Value On

POR

Value On

All Other

Resets

9Fh

VRCON

VREN

VROE

VRR

—

VR3

VR2

VR1

VR0

000- 0000

1Fh

CMCON

C2OUT

C1OUT

—

CIS

CM2

CM1

CM0

00-- 0000

85h

TRISA

—

TRISA4

TRISA3

TRISA2

TRISA1

TRISA0

---1 1111

VREF Output

–

•

VREF

Module

Voltage

Reference

Output

Impedance

(1)

RA2

Note 1: R is dependent upon the Voltage Reference Conﬁguration VRCON<3:0> and VRCON<5>.

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