PIC16C781 datasheet(86/186 Pages) MICROCHIP

86 / 186 page

PIC16C781/782

DS41171A-page 84

Preliminary

 2001 Microchip Technology Inc.

OPAMP CONTROL REGISTER (OPACON: 11Ch)

11.1.2

CALCON REGISTER

The Automatic Calibration Module (ACM) is an internal

state machine which performs an input offset voltage

calibration (trim) on the OPA module (see Figure 11-2).

Calibration

initiated

setting

the

CAL

bit

(CALCON<7>). Upon completion of the calibration

sequence, the ACM will clear the CAL bit.

If a problem arises in the calibration process, the

CALERR flag (CALCON<6>) will be set to indicate the

failure to calibrate.

Setting CALREF (CALCON<5>) forces calibration at a

common mode voltage specified by the output of the

DAC module. The DAC module must be enabled prior

to calibration. Clearing CALREF will perform the cali-

bration with a common mode voltage of 1.2V. The out-

put pin floats during calibration.

R/W-0

U-0

R/W-0

OPAON

CMPEN

—

GBWP

bit 7

bit 0

bit 7

OPAON: OPAMP Enable bit

= OPAMP is enabled

= OPAMP is disabled

bit 6

CMPEN: Comparator Mode Enable bit

= Comparator mode

= OPAMP mode

bit 5-1

Unimplemented: Read as ’0’

bit 0

GBWP: Gain Bandwidth Product Select bits

= 2 MHz typ. (fast mode)

= 70 kHz typ. (slow mode)

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 1: Auto Calibration must be performed while

the module is configured as an OPAMP

(CMPEN = 0). Performing Auto Calibra-

tion function in the Comparator mode

may yield unpredictable results.

2: If the internal 1.2V reference is used for

the common mode voltage during Auto

Calibration, CALREF = 0 (CALCON<5>),

a delay for reference stabilization must be

observed before start of calibration.

3: The OPA module shares pins with the

ADC module. Performing ADC conver-

sions on the OPA+ or OPA- pins may

affect OPAMP stability.

4: When using the DAC as a reference for

calibration, CALREF = 1 (CALCON<5>),

the VDAC voltage must be within the spec-

ified common mode voltage for the

OPAMP.

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