RM0312 datasheet(250/275 Pages) STMICROELECTRONICS

250 / 275 page

ProxSense™ (PXS)

RM0312

250/275

DocID022352 Rev 3

ProxSense™ (PXS)

22.1

Introduction

The ProxSense peripheral measures a capacitance variation so that applications can detect

the proximity or touch of one or more conductive objects when the electrodes are connected

to the PXS pins.

This peripheral operates in Projected mode which is used to measure the charge

transferred by a driven electrode to a second electrode.

Note:

ProxSense

™ is a trademark of Azoteq (Pty) Ltd.

22.2

Main features of the ProxSense peripheral

•

10 independent receiver channels, allowing 10 measurements to be performed in

parallel.

•

Each of the 10 receiver channels can be associated with two different pins, effectively

allowing an application to have up to 20 receiver channels.

•

Each receiver channel can be independently configured to perform projected

capacitance measurements.

•

The size of each CS capacitor can be independently configured with 5 bits of resolution.

•

The size of each electrode parasitic capacitance compensation (EPCC) capacitor can

be independently configured with 8 bits of resolution.

•

The launch of each conversion can be synchronized with an external input, allowing for

very precise measurements in the presence of cyclic disturbances (such as

50 Hz/60 Hz power-supply circuits).

•

End of conversion interrupt, which has an associated interrupt flag, and can wake the

CPU from Active-halt mode.

•

First channel completion interrupt, which has an associated interrupt flag, and can

wake the CPU from Active-halt mode after the first channel has finished its

measurement.

•

The frequency of the clock driving the charge transfer protocol (based on HSI_PXS)

can be scaled from 125 kHz up to 16 MHz.

•

The duration of the UP and PASS phases can be configured independently to optimize

acquisition frequency.

•

The noise detection feature, when enabled, indicates if there was noise during a

previous conversion.

•

Response time can be enhanced by specifying a maximum conversion measurement

value, which is mainly useful for touchkey applications.

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