RM0312 datasheet(254/275 Pages) STMICROELECTRONICS

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ProxSense™ (PXS)

RM0312

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DocID022352 Rev 3

Acquisition initialization

These initializations can be made when the PXS is enabled in PXS_CR1, but not when a

conversion is ongoing.

•

Enable optionally the interrupts, the synchronization feature, and the Rx coupling in

PXS_CR2.

•

Select the mode for the receivers in PXS_RXCR1/2/3. In a standard application, this is

done only once for all acquisitions.

•

Select the state of the pin when the Rx is disabled (inactive) in the PXS_RXINSR

GPIO. For instance, to have PXS_TX0 grounded when inactive, PD0 must be

configured as output low level (PD_DR = 0bxxxxxxx0). To configure TX0 as high

impedance, PD0 must be configured as output open-drain high level (PD_DR =

0bxxxxxxx1).

•

Set the maximum count limit in PXS_MAXR and enable it for the selected receivers in

PXS_MAXENR.

•

Select the sampling capacitor (Cs) size in PXS_RXnCSSELR registers. It is

recommended to select the same Cs size for all receivers belonging to the same

object, especially when a position is interpolated from the measurements of some

receivers (for example, sliders, wheels or screens).

•

Select the receiver group channels A or B in the PXS_CR2 register

•

Select the receivers and the transmitters by setting their corresponding bits

respectively in PXS_RXENR and PXS_TXENR.

•

Select the electrode parasitic capacitance compensation size according to the

acquisition configuration in PXS_RXnEPCCSELR registers. This size has to be

adapted for each couple (Rx, Tx).

The last three actions should be repeated before each acquisition with a different

transmitter.

22.5.3

PXS acquisition launching

Manual start

The acquisition is launched on all enabled receivers in parallel by setting the START bit in

PXS_CR1.

Synchronized start

To synchronize an acquisition with an external signal connected to the PXS_TRIG pin, the

SYNC feature must be enabled and the signal edge selected in PXS_CR2. The acquisition

is enabled by setting the START bit in PXS_CR1 and the acquisition starts on the next

occurrence of the selected edge on the PXS_TRIG pin. Once a synchronized acquisition is

completed, the START bit must be set again to start a new acquisition.

The start cannot be synchronized during Active-halt mode as transitions on the PXS_TRIG

input are not recognized during Active-halt mode.

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