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NRF52820-QDAA-R Datasheet(PDF) 149 Page - Nordic Semiconductor |
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NRF52820-QDAA-R Datasheet(HTML) 149 Page - Nordic Semiconductor |
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149 / 437 page  Peripherals If the SAMPLEPER value needs to be changed, the QDEC shall be stopped using the STOP task. SAMPLEPER can be then changed upon receiving the STOPPED event, and QDEC can be restarted using the START task. Failing to do so may result in unpredictable behavior. It is good practice to only change registers LEDPOL, REPORTPER, DBFEN, and LEDPRE when the QDEC is stopped. When started, the decoder continuously samples the two input waveforms and decodes these by comparing the current sample pair (n) with the previous sample pair (n-1). The decoding of the sample pairs is described in the table below. Previous sample pair(n - 1) Current samples pair(n) SAMPLE register ACC operation ACCDBL operation Description A B A B 0 0 0 0 0 No change No change No movement 0 0 0 1 1 Increment No change Movement in positive direction 0 0 1 0 -1 Decrement No change Movement in negative direction 0 0 1 1 2 No change Increment Error: Double transition 0 1 0 0 -1 Decrement No change Movement in negative direction 0 1 0 1 0 No change No change No movement 0 1 1 0 2 No change Increment Error: Double transition 0 1 1 1 1 Increment No change Movement in positive direction 1 0 0 0 1 Increment No change Movement in positive direction 1 0 0 1 2 No change Increment Error: Double transition 1 0 1 0 0 No change No change No movement 1 0 1 1 -1 Decrement No change Movement in negative direction 1 1 0 0 2 No change Increment Error: Double transition 1 1 0 1 -1 Decrement No change Movement in negative direction 1 1 1 0 1 Increment No change Movement in positive direction 1 1 1 1 0 No change No change No movement Table 49: Sampled value encoding 6.11.2 LED output The LED output follows the sample period. The LED is switched on for a set period before sampling and then switched off immediately after. The period the LED is switched on before sampling is given in the LEDPRE register. The LED output pin polarity is specified in the LEDPOL register. When using off-chip mechanical encoders not requiring an LED, the LED output can be disabled by writing value 'Disconnected' to the CONNECT field of the PSEL.LED register. In this case, the QDEC will not acquire access to a pin for the LED output. 6.11.3 Debounce filters Each of the two-phase inputs have digital debounce filters. When enabled through the DBFEN register, the filter inputs are sampled at a fixed 1 MHz frequency during the entire sample period (which is specified in the SAMPLEPER register). The filters require all of the samples within this sample period to equal before the input signal is accepted and transferred to the output of the filter. As a result, only input signal with a steady state longer than twice the period specified in SAMPLEPER are guaranteed to pass through the filter. Any signal with a steady state shorter than SAMPLEPER will always 4463_156 v1.0 149 |
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