ZUSBOPTSC01ZACG datasheet(146/282 Pages) ZILOG

146 / 282 page

PS022827-1212

P R E L I M I N A R Y

Operation

Z8 Encore! XP® F082A Series

Product Specification

129

Calibration and Compensation

The Z8 Encore! XP F082A Series ADC is factory calibrated for offset error and gain error,

with the compensation data stored in Flash memory. Alternatively, you can perform your

own calibration, storing the values into Flash themselves. Thirdly, the user code can per-

form a manual offset calibration during DIFFERENTIAL Mode operation.

Factory Calibration

Devices that have been factory calibrated contain 30 bytes of calibration data in the Flash

option bit space. This data consists of 3 bytes for each input mode, one for offset and two

for gain correction. For a list of input modes for which calibration data exists, see the

Zilog Calibration Data section on page 168.

User Calibration

If you have precision references available, its own external calibration can be performed

using any input modes. This calibration data takes into account buffer offset and nonlin-

earity; therefore Zilog recommends that this calibration be performed separately for each

of the ADC input modes planned for use.

Manual Offset Calibration

When uncalibrated, the ADC has significant offset (see Table 139 on page 236). Subse-

quently, manual offset calibration capability is built into the block. When the ADC Con-

trol Register 0 sets the input mode (ANAIN[2:0]) to MANUAL OFFSET

CALIBRATION Mode, the differential inputs to the ADC are shorted together by an inter-

nal switch. Reading the ADC value at this point produces 0 in an ideal system. The value

actually read is the ADC offset. This value can be stored in nonvolatile memory (see the

Nonvolatile Data Storage chapter on page 176) and accessed by user code to compensate

for the input offset error. There is no provision for manual gain calibration.

Software Compensation Procedure Using Factory Calibration Data

The value read from the ADC high and low byte registers is uncompensated. The user

mode software must apply gain and offset correction to this uncompensated value for

maximum accuracy. The following equation yields the compensated value:

where GAINCAL is the gain calibration value, OFFCAL is the offset calibration value and

ADCuncomp is the uncompensated value read from the ADC. All values are in two’s com-

plement format.

ADC

comp

ADC

uncomp

OFFCAL

–



ADC

uncomp

OFFCAL

–

 GAINCAL



 2



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