at42qt1481 ATMEL Corporation, at42qt1481 Datasheet - Page 28

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

4.5
4.6
4.7
28
Cal All – 0x03
Force Reset – 0x04
QT1481 Overview – 0x06
AT42QT1481
The low level calibration and offset procedure involves the device calibrating each key in turn at
each of the operating frequencies selected with FREQ0, FREQ1 and FREQ2, calculating the
difference between the signals at those frequencies and storing the results as offsets into
CFO_1 and CFO_2 for each key. When the procedure is complete, the host can read back the
setups and record CFO_1 and CFO_2 into its own copy of the setups block. The QT1481 does
not change the Setups CRC, so there will be a mismatch in the Setups CRC after this command
completes. The onus is on the host to compute the CRC and upload a definitive Setups block to
the QT1481.
This command must be repeated twice within 110 ms or the command fails. The repeating
command must be sequential without any intervening command.
After the second 0x03 from the host, the QT1481 replies with the character 0xFC. Shortly
thereafter the QT1481 recalibrates all keys and restarts operation.
If no 0xFC comes back, the command was not properly received and the QT1481 should
preferably be reset.
The host can monitor the progress of the recalibration by checking the QT1481 status byte,
using command 0x06, during the course of the calibration.
A key shows an error flag (using command 0x8k) indicating the key calibration failed if the
reference did not successfully converge with the signal average, or if its signal is below the low
signal threshold.
The command must be repeated twice within 110 ms or the command fails. The repeating
command must be sequential without any intervening command. After the second 0x04, the
QT1481 replies with the character 0xFB just prior to executing the reset operation.
After any reset, the QT1481 automatically performs a full key calibration on all keys.
The host can monitor the progress of the reset to see when the chip is operating again by
checking the QT1481 status byte for recalibration by repeatedly issuing command 0x06 (see
Section 4.7 on page
Reports the EN60730 counters, a QT1481 status byte, and the first key declaring detect. The
STATUS pin becomes inactive on processing this command, if it was made active by a key touch
(or release).
This command returns five individual data bytes, plus two CRC bytes, in the sequence:
A 16-bit CRC is appended to the response; this CRC folds in the command 0x06 itself initially.
1. Device Status
2. Touch Overview
3. 100 ms Counter (for EN60730 compliance)
4. Matrix Scan Counter (for EN60730 compliance)
5. Signal Fail Counter (for EN60730 compliance)
28).
9621B–AT42–06/11