AN2549

Modified features

9/33

Note:

sink on this pin on the ST10F272Z2 compared to the ST10F269Zx, it is recommended not

to connect a resistor (for example, because of an RC filter), to prevent creating an offset in

the reference.

1.4.3

Software impact

Self-calibration and ADC initialization routine

An automatic self-calibration adjusts the ADC module to process parameter variations at

each reset event. After reset, the busy flag (read-only) ADBSY is set because the self-

calibration is ongoing. The duration of self-calibration depends on the CPU clock: It may

take up to 40.629 ± 1 clock pulses. The user must poll this bit to know when self-calibration

is complete in order to initialize the ADC module.

This self-calibration is seen by the ST10F272Z2 as a conversion and thus bit ADCIR is set.

The software should perform a dummy read of the ADDAT register and clear the ADCIR and

ADCEIR flags before configuring the ADC module and starting the first conversion.

New bit ADOFF, bit 6 of ADCON register

The bit 6 of the ADCON register, reserved in previous ST10 devices, is now used to enable

and disable the ADC. By default this bit is cleared and the ST10F272Z2 is compatible with

the ST10F269Zx. Therefore, there is no impact on the software, provided that this bit is not

written to.

Reference supply

current

Running mode

Power-down mode

-

-

500

1

-

-

5000

1

µA

µA

DNL

Differential nonlinearity

-0.5

+0.5

-1

+1

LSB

INL

Integral nonlinearity

-1.5

+1.5

-1.5

+1.5

LSB

OFS

Offset error

-1.0

+1.0

-1.5

+1.5

LSB

Table 6.

ADC differences (continued)

Symbol

Parameter

Limit values for ST10F269Zx

Limit values for ST10F272Z2

Unit

Min

Max

Min

Max

ADCON (FFA0h / A0h)

SFR

Reset value: 0000h

15

14

13

12

11

10

9

8

765

4321

0

ADCTC

ADSTC

AD

CRQ

AD

CIN

AD

WR

AD

BSY

AD

ST

AD

OFF

ADM

ADCH

R/W

R/W

R/W

R/W

R/W

RO

R/W

R/W

R/W

R/W

Table 7.

ADCON register description

Bit

Function

Comment

ADOFF

ADC Disable

0: Analog circuitry of A/D converter is on

1: Analog circuitry of A/D converter is turned off

New bit valid only for the

ST10F272Z2.

Reserved on ST10F269Zx.