16F506 datasheet(51/114 Pages) MICROCHIP

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Preliminary

DS41268B-page 49

PIC12F510/16F506

8.0

COMPARATOR VOLTAGE

REFERENCE MODULE

(PIC16F506 ONLY)

The Comparator Voltage Reference module also

allows the selection of an internally generated voltage

reference for one of the C2 comparator inputs. The

VRCON register (Register 8-1) controls the Voltage

Reference module shown in Figure 8-1.

8.1

Configuring The Voltage

Reference

The voltage reference can output 32 voltage levels; 16

in a high range and 16 in a low range.

Equation 8-1 determines the output voltages:

EQUATION 8-1:

8.2

Voltage Reference Accuracy/Error

The full range of VSS to VDD cannot be realized due to

construction of the module. The transistors on the top

and bottom of the resistor ladder network (Figure 8-1)

keep CVREF from approaching VSS or VDD. The excep-

tion is when the module is disabled by clearing the

VREN bit (VRCON<7>). When disabled, the reference

voltage is VSS when VR<3:0> is ‘0000’ and the VRR

(VRCON<5>) bit is set. This allows the comparator to

detect a zero-crossing and not consume the 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 ref-

erence can be found in Section 13.2 “DC Character-

istics: PIC12F510/16F506 (Extended)”.

VRCON: PIC16F506 ONLY (ADDRESS: 0Ch)

VRR = 1 (low range): CVREF = (VR3:VR0/24) x VDD

VRR = 0 (high range):

CVREF = (VDD/4) + (VR3:VR0 x VDD/32)

R/W-0

R/W-1

U-0

R/W-1

VREN

VROE

VRR

—

VR3

VR2

VR1

VR0

bit 7

bit 0

bit 7

VREN: CVREF Enable bit

= CVREF is powered on

= CVREF is powered down, no current is drawn

bit 6

VROE: CVREF Output Enable bit(1)

= VREF output is enabled

= VREF output is disabled

bit 5

VRR: CVREF Range Selection bit

= Low range

= High range

bit 4

Unimplemented: Read as ‘0’

bit 3-0

VR<3:0> CVREF Value Selection bit

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

When VRR = 0: CVREF= VDD/4+(VR<3:0>/32)*VDD

Note 1: When this bit is set, the TRIS for the VREF pin is overridden and the analog voltage

is placed on the VREF pin.

2: VREF controls for ratio metric reference applies to Comparator 2 on the PIC12F506

only.

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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