ST7MC1 datasheet(236/308 Pages) STMICROELECTRONICS

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10-BIT A/D CONVERTER (ADC) (Cont’d)

10.8.3.3 Digital A/D Conversion Result

The conversion is monotonic, meaning that the re-

sult never decreases if the analog input does not

and never increases if the analog input does not.

If the input voltage (VAIN) is greater than VREF+

(high-level voltage reference) then the conversion

result is FFh in the ADCDRMSB register and 03h

in the ADCDRLSB register (without overflow indi-

cation).

If the input voltage (VAIN) is lower than VREF- (low-

level voltage reference) then the conversion result

in the ADCDRMSB and ADCDRLSB registers is

00 00h.

The A/D converter is linear and the digital result of

the conversion is stored in the ADCDRMSB and

ADCDRLSB registers. The accuracy of the con-

version is described in the Electrical Characteris-

tics Section.

RAIN is the maximum recommended impedance

for an analog input signal. If the impedance is too

high, this will result in a loss of accuracy due to

leakage and sampling not being completed in the

alloted time.

RREF is the value of the resistive bridge imple-

mented in the device between VREF+ and VREF-.

10.8.3.4 A/D Conversion

The analog input ports must be configured as in-

put, no pull-up, no interrupt. Refer to the «I/O

ports» chapter. Using these pins as analog inputs

does not affect the ability of the port to be read as

a logic input. If the application used the high-im-

pedance analog inputs, then the sample time

should be stretched by setting the ADSTS bit in

the MCCBCR register.

In the ADCCSR register:

– Select the CS[3:0] bits to assign the analog

channel to convert.

ADC Conversion mode

In the ADCCSR register:

– Set the ADON bit to enable the A/D converter

and to start the conversion. From this time on,

the ADC performs a continuous conversion of

the selected channel.

– The EOC bit is kept low by hardware during the

conversion.

Note: Changing the A/D channel during conver-

sion will stop the current conversion and start con-

version of the newly selected channel.

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