PCINT13 datasheet(201/294 Pages) ATMEL

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9219A–RFID–01/11

Atmel ATA5505 [Preliminary]

17.2.2

Current Source for Low Cost Transducer

An external transducer based on a variable resistor can be connected to the Current Source.

This can be, for instance:

• A thermistor, or temperature-sensitive resistor, used as a temperature sensor,

• A CdS photoconductive cell, or luminosity-sensitive resistor, used as a luminosity sensor,

•...

Using the Current Source with this type of transducer eliminates the need for additional parts

otherwise required in resistor network or Wheatstone bridge.

17.2.3

Voltage Reference for External Devices

An external resistor used in conjunction with the Current Source can be used as voltage refer-

ence for external devices. Using a resistor in series with a lower tolerance than the Current

Source accuracy (

≤ 2%) is recommended. Table 17-2 gives an example of voltage references

using standard values of resistors.

17.2.4

Threshold Reference for Internal Analog Comparator

An external resistor used in conjunction with the Current Source can be used as threshold ref-

erence for internal Analog Comparator (See ”AnaComp - Analog Comparator” on page 222.).

This can be connected to AIN0 (negative Analog Compare input pin) as well as AIN1 (positive

Analog Compare input pin). Using a resistor in series with a lower tolerance than the Current

Source accuracy (

≤ 2%) is recommended. Table 17-2 gives an example of threshold refer-

ences using standard values of resistors.

17.3

Control Register

17.3.1

AMISCR – Analog Miscellaneous Control Register

• Bit 0 – ISRCEN: Current Source Enable

Writing this bit to one enables the Current Source as shown in Figure 17-1. It is recommended

to use DIDR register bit function when ISRCEN is set. It also recommended to turn off the Cur-

rent Source as soon as possible (e.g. once the ADC measurement is done).

Bit

5432

AREFEN

XREFEN

ISRCEN

AMISCR

Read/Write

RRRR

R/W

Initial Value

0000

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