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QT60325-AS Datasheet(PDF) 8 Page - Quantum Research Group |
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QT60325-AS Datasheet(HTML) 8 Page - Quantum Research Group |
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8 / 42 page  being checked be first fully recalibrated in order to allow the Cz and DAC offset values to alter. If a key is outside of a limit, either of bits 2 and 3 of command 'e' will be set for that key. The error will also appear as an error in a bitfield reported with command 'E'. There is no mechanism by which keys will automatically recalibrate if the reference drifts past a guardband boundary. 2.9 Adjacent Key Suppression (AKS™) See also command ^P, page 27 QT60xx5 devices incorporate adjacent key suppression (‘AKS’ - patent pending) that can be selected on a per-key basis. AKS permits the suppression of multiple key presses based on relative signal strength. This feature assists in solving the problem of surface moisture which can bridge a key touch to an adjacent key, causing multiple key presses. This feature is also useful for panels with tightly spaced keys, where a fingertip might inadvertently activate an adjacent key. AKS works for keys that are AKS-enabled anywhere in the matrix and is not restricted to physically adjacent keys; the device has no knowledge of which keys are actually physically adjacent. When enabled for a key, adjacent key suppression causes detections on that key to be suppressed if any other AKS-enabled key in the panel has a more negative signal deviation from its reference. This feature does not account for varying key gains (burst length) but ignores the actual negative detection threshold setting for the key. If AKS-enabled keys in a panel have different sizes, it may be necessary to reduce the gains of larger keys relative to smaller ones to equalize the effects of AKS. The signal threshold of the larger keys can be altered to compensate for this without causing problems with key suppression. Adjacent key suppression works to augment the natural moisture suppression of narrow gated transfer switches (Section 3.13), creating a more robust sensing method. 2.10 Full Recalibration See also command ‘b’, page 28 The devices fully recalibrate on powerup, after a hard reset, a soft reset or after a recalibrate ‘b’ command using an algorithm that seeks out the optimal level of R2R offset and Cz cancellation on a per-key basis. After powerup or a reset the matrix is scanned key by key and appropriate calibrations are set for each in accordance with user-defined setup information. Since the circuit can tolerate a very wide signal range, it is capable of adapting to a wide mix of key sizes and shapes having widely varying Cx coupling capacitances. If a false calibration occurs due to a key touch or foreign object on the keys during powerup, the affected key will recalibrate again when the object is removed depending on the settings of Positive Threshold and Positive Recal Delay (Sections 2.2 and 2.7). Full recalibration is distinct from fast-recalibration, wherein only the Reference level is quickly adjusted. Full recalibration requires 26 burst cycles to complete whereas fast recalibration requires only one cycle (Section 2.5). The time required for recalibration is dependent on the burst spacing setting ^G (Section 3.8). Individual keys or groups of keys can be recalibrated with a single command depending on the current command scope. The time required to recalibrate many keys is not multiplicative; the cal process for multiple keys runs in parallel. 2.11 Boundary Error Reporting See also commands ‘e’, page 23; ^N, page 27 Unlike guardband error reporting, boundary error reporting only works within the active ADC signal window segment in which the key's signal resides. Complex factoring of Cz and Offset are not required for these tests, and the tests do not require that the key be recalibrated to see the error condition. Drift compensation can cause a key's reference level to move near to the border of the ADC's 8-bit signal window; this may make a key inoperable if the reference pegs near zero, depriving the signal of the ability to move further negative when a key is touched. Normally the reference level should be reasonably centered within the ADC's current range, i.e. at a level of about 128 decimal / 0x80 hex. The truth logic for reference level drift error reporting is: e/b2 = Reference > 191 e/b3 = Reference < 64 where e/b2 is command 'e' bit 2, and e/b3 is command 'e' bit 3. If either bit is set, the key should be recalibrated using command 'b'. Note that guardbanding errors (Section 2.8) also use these same bits for error reporting, but guardbanding does not usually affect these bits until after a recalibration. Each Reference Boundary error will also appear as an error in a bitfield reported from command 'E'. There is no mechanism by which keys can be made to automatically recalibrate if the reference drifts past a window boundary. 2.12 Device Status & Reporting See also commands ‘7’, page 22; ‘e’, page 23; ‘E’, page 23; ‘k’, page 23, ‘K’, page 24 The device can report on the general device status or specific key states including touches and error conditions, depending on the command used. Usually it is most efficient to periodically request the general device status using command ‘7’ first, as the response to this command is a single byte which reports back on behalf of all keys. ‘7’ indicates if there are any keys detecting, calibrating, or in error. If command ‘7’ reports a condition requiring further investigation, the host device can then use commands ‘e’, ‘E’, ‘k’ or ‘K’ to provide further details of the event(s) in progress. This hierarchical approach provides for a concise information flow using minimal data transfers and low host software overhead. Bit 4 of command 7 reports if there is a discrepancy between the eeprom and the Flash ROM backup of the eeprom in case of data corruption; it is also set whenever a Setup parameter has changed but was not yet been copied into Flash. See Section 4.6. Resetting the device will force the eeprom changes to be copied to Flash if legitimate, or it will © Quantum Research Group Ltd. lQ 8 www.qprox.com QT60xx5 / R1.05 |
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