MPR121 datasheet(15/57 Pages) FREESCALE

15 / 57 page

MPR121

Sensors

Freescale Semiconductor

FILTER CONFIGURATION REGISTER

Figure 9. Filter Configuration Register

The SFI, ESI and FFI are described in AN3890. In addition to these global (same for all electrodes) settings, the MPR121

electrodes can also be independently configured.

ELECTRODE CHARGE CURRENT REGISTER

Figure 10. Electrode Charge Current Register

543210

CDT

SFI

ESI

Reset:

000000

= Unimplemented

Table 10. Filter Configuration Register Field Descriptions

Field

Description

7:5

CDT

Charge Discharge Time – The Charge Discharge Time field selects the amount of

time an electrode charges and discharges.

000 Encoding 0 – Invalid

001 Encoding 1 – Time is set to 0.5

μs

010 Encoding 2 – Time is set to 1

μs

111 Encoding 7 – Time is set to 32

μs.

4:3

SFI

Second Filter Iterations – The Second Filter Iterations field selects the number of

samples taken for the second level filter.

00 Encoding 0 – Number of samples is set to 4

01 Encoding 1 – Number of samples is set to 6

10 Encoding 2 – Number of samples is set to 10

11 Encoding 3 – Number of samples is set to 18

2:0

ESI

Electrode Sample Interval – The Electrode Sample Interval field selects the period

between samples used for the second level of filtering.

000 Encoding 0 – Period set to 1 ms

001 Encoding 1 – Period set to 2 ms

111 Encoding 7 – Period set to 128 ms

543210

CDC

Reset:

000000

= Unimplemented

Table 11. Electrode Charge Current Register Field Descriptions

Field

Description

5:0

CDC

Electrode # Charge Discharge Current – The Charge Discharge Current field

selects the supply current to be used when charging and discharging an electrode.

000000 Encoding 0 – Disables Electrode Charging

000001 Encoding 1 – Sets the current to 1

μA

111111 Encoding 63 – Sets the current to 63

μA

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