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AT42QT1110-AU Datasheet(PDF) 20 Page - ATMEL Corporation |
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AT42QT1110-AU Datasheet(HTML) 20 Page - ATMEL Corporation |
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20 / 50 page  20 AT42QT1110-MU / AT42QT1110-AU [DATASHEET] 9520J–AT42–05/2013 Figure 4-9. Guard Channel Example 4.10 Self-test Functions 4.10.1 Internal Hardware Tests Internal hardware tests check for hardware failure in the device internal memory areas and data paths. Any failure detected in the function or contents of application ROM, RAM or registers causes the device to reset itself. The application code is scanned with a CRC check routine to confirm that the application data is all correct. The RAM and registers are checked periodically (every 10 seconds) for dynamic and static failures. 4.10.2 Functional Checks Functional checks confirm that the device is operating within expected parameters; any failure detected in these tests is notified to the system host. The device will continue to operate in the event that such functional failures are detected. The functional tests are: Check that the channel-measurement signals are within the defined range. Confirm that data stored in the EEPROM is valid. These tests are carried out as the particular functions are used. For example, the EEPROM is checked when the device attempts to load data from EEPROM, and the channel signals are checked when a measurement is carried out. Note: If a particular channel is unused, the threshold of that channel should be set to 0 to prevent the incorrect reporting of the unused channel as being in an error state. 4.11 Signal Processing 4.11.1 Detection Integrator The device features a detection integration mechanism, which acts to confirm a detection in a robust fashion. A per- key counter is incremented each time the key has exceeded its threshold. When this counter reaches a preset limit the key is finally declared to be touched. For example, if the DI limit is set to 10, then a key signal must fall by more than the key threshold, and remain below that level for 10 acquisitions, before the key is declared to be touched. Similarly, the DI is applied to a key that is going out of detect: it must take 10 acquisitions where the signal has not exceeded its detect threshold before it is declared to leave touch. 4.11.2 Burst Length Limitations The maximum burst length is 2048 pulses. The recommended design is to use a capacitor that gives a signal of <1000 pulses. The number of pulses in the burst can be obtained by reading the key signal (that is, the number of pulses to complete measurement of the key signal) over the SPI interface (see Section 6.8 on page 26). Alternatively, a scope can be used to measure the entire burst, and then the burst length divided by the time for a single pulse. Guard Channel Formed of One Key Key Pad Formed of Six Keys |
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