at42qt1481 ATMEL Corporation, at42qt1481 Datasheet - Page 33

• Manufacturer Part Number: at42qt1481
• Description: 48-key Qmatrix Ic
• Manufacturer: ATMEL Corporation

4.17
4.18
4.19
9621B–AT42–06/11
Status for Key “k” – 0x8k
Cal Key “k” – 0xck
Command Sequencing
Returns a bit-field for key “k” where k is from 0 – 47. The bit-field is explained in
Table 4-4.
Bit 4 (FMEA KGTT) will be set during calibration after reset, and should be ignored until
calibration has completed. A 16-bit CRC is appended to the response. This CRC folds in the
command 0x8k itself initially.
This command must be repeated twice within 110 ms or the command fails. The repeating
command must be sequential without any intervening command.
This command functions the same as the 0x03 Cal All command except that this command only
affects one key “k” where “k” is from 0 to 47.
The chosen key “k” is recalibrated in its native timeslot. Normal running of the part is not
interrupted and all other keys operate correctly throughout. This command is for use only during
normal operation to try to recover a single key that has failed or is not calibrated correctly.
Returns the 1’s complement of 0xck just before the key is recalibrated.
To interface the QT1481 with a host, the flow diagram of
The actual settings of the Setups block used should normally just be the default settings except
where changes are specifically required, such as for sensitivity, timing, or AKS changes.
The circles in this drawing are communications interchanges between host and sensor. The
rectangles are internal host states or processing events. If any communications exchange fails,
either the QT1481 fails to respond within the allotted time, or the response CRC is incorrect, or
the response is out of context (the response is clearly not for the intended command). In these
cases the host should just repeat the command.
The control flow spends 99 percent of its time alternating between the two states within the
dashed rectangle. If a key is detected, the control flow enters Key Detection Processing.
Stuck Key Detection processing (0xck) is optional, since the QT1481 contains the max
on-duration timeout function and can therefore recalibrate the stuck key automatically. However,
the host can recalibrate stuck keys with greater flexibility if the recalibration timeouts are set to
infinite and the host recalibrates them under specific conditions.
Bit
7
6
5
4
3
2
1
0
Status for Key “k”
Description
1 = Reserved
1 = Reserved
1 = Reserved
1 = FMEA KGTT test failed for this key
1 = Key is in detect
1 = Signal ref < LSL (low signal error). See
1 = Key is undergoing calibration
1 = Calibration on this key failed
Section 5.18 on page
Figure 4-1 on page 35
AT42QT1481
48.
Table
is suggested.
4-4:
33