MPR121_10 FREESCALE [Freescale Semiconductor, Inc], MPR121_10 Datasheet - Page 19

• Manufacturer Part Number: MPR121_10
• Description: Proximity Capactive touch Senosr controller
• Manufacturer: FREESCALE [Freescale Semiconductor, Inc]

Sensors
Freescale Semiconductor
the AFE Configuration Register is different, it must be changed to match. For a description of this register, please refer to AN3890.
The RETRY is disabled because in production systems, this will not be required. The BVA is set to 10 which allows the baseline
to be updated. 10 is used instead of 11 because this guarantees that the baseline will be lower than the data. This is preferable
as it protects against false touches. If somehow the baseline started higher than the data, a touch would be triggered and the
detection system would have to be reset to work correctly. Last, both the automatic configuration and automatic reconfiguration
are enable. Reconfiguration will trigger any time the baseline drifts outside the range set by the USL and the LSL.
cannot occur without the USL, LSL and TSL being incorrectly set. The most likely configuration error is to set the USL (upper
limit) at a lower value than the LSL (lower limit). Thus, as the algorithm searches for settings that work, it would always result in
a fail throwing the OOR (Out Of Range) status flag.
calibration, the ACFF will trigger. If the fail occurs during a reconfiguration, the ARFF will trigger.
ELE0-7 OUT OF RANGE STATUS REGISTER
The normal setup of the system is to set this register to 0x0B or 0b00001011. This means that the FFI is 00, but if the FFI in
There is also a set of flags which show when the automatic configuration has failed. For normal sized touch electrodes, this
The ARFF and ACFF also tell the user which type of configuration cycle caused the error. If it was triggered during an initial
Table 17. AUTO-CONFIG Control Register Field Descriptions
Reset:
RETRY
W
R
AFES
Field
BVA
ARE
ACE
7:6
5:4
3:2
1
0
E7S
7
0
First Filter Iterations – The first filter iterations field selects the number of samples taken
as input to the first level of filtering. This value must match the FFI set in the AFE
Configuration register for proper AUTO-CONFIG functionality.
00 Encoding 0 – Sets samples taken to 6
01 Encoding 1 – Sets samples taken to 10
10 Encoding 2 – Sets samples taken to 18
11 Encoding 3 – Sets samples taken to 34
Retry – The Retry value determines under what circumstances the auto-configuration
system will retry.
00 – Retry disabled
01 – Retry enabled
10 – Retry enabled
11 – Retry enabled
Baseline Value Adjust – The baseline value adjust determines the initial value of the
baseline registers after auto-configuration completes.
00 – Baseline is not changed
01 – Baseline is cleared
10 – Baseline is set to the AUTO-CONFIG baseline with the lower 3 bits cleared
11 – Baseline is set to the AUTO-CONFIG baseline
Automatic Reconfiguration Enable – The automatic reconfiguration enable, enables or
disables automatic reconfiguration.
0 – ARE is disabled
1 – ARE is enabled
Automatic Configuration Enable – The automatic configuration enable, enables or
disables automatic configuration.
0 – ACE is disabled
1 – ACE is enabled
= Unimplemented
Figure 16. ELE0-7 Out Of Range Status Register
E6S
6
0
E5S
5
0
E4S
4
0
Description
E3S
3
0
E2S
2
0
E1S
1
0
E0S
0
0
MPR121
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