RM0312 datasheet(255/275 Pages) STMICROELECTRONICS

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RM0312

ProxSense™ (PXS)

273

22.5.4

PXS acquisition result

The application can check that the acquisition is fully completed by polling the EOCF bit in

PXS_ISR. Alternatively, the application can poll the FCCF bit in PXS_ISR to find out when

at least one channel has finished its acquisition. Otherwise, instead of polling EOCF or

FCCF, the corresponding interrupts can be enabled. If the PXS_RXSR and PXS_RXENR

registers are identical, all the selected Rx have been successfully acquired. Each channel

result is available in PXS_RXnCNTR.

The status flags EOCF and FCCF in PXS_ISR are cleared by setting the START bit in

PXS_CR1 again.

If the noise detection is enabled, its flag must be checked before processing the data.

22.5.5

Stopping a PXS acquisition

The only way to stop a conversion which is in progress is by writing ‘0’ to PXSEN. In this

case, the results of the conversion which was stopped prematurely are not guaranteed.

Caution:

CIPF can stay at ‘1’ for as long as 8 µs after PXSEN is cleared.

22.6

Special features

22.6.1

Sampling capacitor selection

As the sampling capacitors are built-in, their size can be adapted to the connected

electrode. 32 sizes of sampling capacitances (CS) can be selected for each receiver using

the PXS_RXnCSSELR register.

22.6.2

EPCC selection

The electrode parasitic capacitance compensation (EPCC) first fine-tunes the CS

capacitance value so that all receiver conversion results are close to the same targeted

value. Second, it can be used to compensate for changes in the environment conditions.

This compensation makes the system more sensitive to changes and thus smaller

capacitance changes on the electrode can be detected.

The EPCC size is adjusted in the PXS_RXnEPCCSELR register.

22.6.3

RF detection

Besides on-chip protection which prevents RF contamination, the product provides a feature

to detect RF interference.

An antenna has to be connected to the PXS_RFIN pin, and the NOISEDETEN bit must be

set in the PXS_CR2 register before enabling the ProxSense by setting PXS_EN bit in

PXS_CR1. Then, after each acquisition, the application can check the NOISEDETF bit in

the PXS_ISR register to verify if the results should be discarded. The NOISEDETF bit must

be reset by the application.

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