AN1711 datasheet(6/40 Pages) STMICROELECTRONICS

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SOFTWARE TECHNIQUES FOR COMPENSATING ST7 ADC ERRORS

1.5 READING THE ADC CONVERSION RESULTS

It is recommended to read the ADCDRL first and then the ADCDRH. When the ADC is in con-

tinuous mode, the EOC is set at the end of conversion and a new conversion is started again

(unless the ADC supports one-shot conversion).

The ADC conversion results are not latched on ADCDRL and ADCDRH. This means that if,

between reading ADCDRL and ADCDRH, there is an interrupt which takes a lot of time (more

than the ADC conversion time), then the software will read the ADCDRL from one conversion

and the ADCDRH from another conversion. It is thus recommended to disable interrupts be-

fore reading the conversion results from ADCDRL and ADCDRH and then enable interrupts

again.

However, if you are reading the ADC registers (ADCDRL and ADCDRH) in a peripheral inter-

rupt subroutine, for example, if you are reading the registers in a timer interrupt or external in-

terrupt sub-routine then, do not disable and enable the interrupts.

The “Enable Interrupt” instruction in an interrupt subroutine (in concurrent interrupt mode) will

enable interrupts and cause a nested mode interrupt.

1.6 ENTERING HALT MODE

It is always recommended to shut down the ADC before entering the HALT mode. When ex-

iting from HALT mode, put the ADC ON again. The stabilization time for the ADC, after exiting

from HALT is specified in the datasheet.

1.7 USING A TIMER TO MAKE PERIODIC CONVERSIONS

Some applications may have special requirements for ADC conversion. For example, in an

audio application, you may need to sample an audio signal of maximum 3 kHz. You can

choose to sample 6K samples per second or higher (12K samples/s or 24K samples/s). The

ST7 ADCs do not have a feature for doing this.

In this case it is recommended to use the timer and configure it to generate 6K interrupts (or

12K/ 24K depending on the design) per second. In your timer interrupt routine, the ADC con-

version results can be read and stored.

This kind of configuration is easy to use because of the very fast conversion time of ST7 ADCs

and the built-in continuous conversion feature.

AN1711 Datasheet(PDF) 6 Page - STMicroelectronics