ST72C171 datasheet(46/152 Pages) STMICROELECTRONICS

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ST72C171

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OP-AMP MODULE (Cont’d)

VOLTAGE REFERENCE CONTROL REGISTER

(OAVRCR)

Read/Write

Reset value: 0000 0000 (00h)

Bit 7 = VR2E:

VR2 Enable

This bit is set and reset by software. When the ref-

ererence voltage is selected (PS2[1:0] = 00 in the

OA2CR register) it connects VSSA (analog ground)

or Reference Voltage 2 (VR2) to the OA2 positive

input.

0: OA2 positive input is connected to VSSA

1: OA2 positive input is connected to VR2 voltage

value

Bit 6:4 = VR2[2:0]

Voltage selection for channel 2

of the 8-step reference voltage

These bits are set and reset by software, they

specify the Reference Voltage 2 (VR2) connected

to the OA2 positive input when PS2[1:0] = 00 in

the OA2CR register

Bit 3= VR1E

VR1 Enable

This bit is set and reset by software. When the ref-

ererence voltage is selected (PS1[1:0] = 00 in the

OA1CR register) it connects VSSA (analog ground)

or Reference Voltage 1 (VR1) to the OA1 positive

input.

0: OA1 positive input is connected to VSSA

1: OA1 positive input is connected to VR1 voltage

value

Bit 2:0 - VR1[2:0]

Voltage selection for channel 1

of the 8-step reference voltage

These bits are set and reset by software, they

specify the Reference Voltage 1 (VR1) connected

to the OA1 positive input when PS1[1:0] = 00 in

the OA1CR register

Note: When both VR2E and VR1E are reset, the

8-step voltage reference cell is disabled and en-

ters low power mode.

VR2E

VR22

VR21

VR20

VR1E

VR12

VR11

VR10

Reference

Voltage 2

VR2E

VR22

VR21

VR20

0 (VSSA)0

VDDA/8

100

2 x VDDA/8

100

3 x VDDA/8

101

4 x VDDA/8

101

5 x VDDA/8

110

6 x VDDA/8

110

7 x VDDA/8

111

VDDA

111

Reference

Voltage 1

VR1E

VR12

VR11

VR10

0 (VSSA)

xxx

VDDA/8

2 x VDDA/8

3 x VDDA/8

4 x VDDA/8

5 x VDDA/8

6 x VDDA/8

7 x VDDA/8

VDDA

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