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NRF52811-QCAA-R Datasheet(PDF) 167 Page - Nordic Semiconductor |
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NRF52811-QCAA-R Datasheet(HTML) 167 Page - Nordic Semiconductor |
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167 / 444 page  Peripherals It is good practice to change other registers (LEDPOL, REPORTPER, DBFEN and LEDPRE) only 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 55: Sampled value encoding 6.13.2 LED output The LED output follows the sample period, and the LED is switched on a given period before sampling and switched off immediately after the inputs are sampled. 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. For using off-chip mechanical encoders not requiring a 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 LED output pin and the pin can be used for other purposes by the CPU. 6.13.3 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), and 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, and any signal with a steady state shorter than SAMPLEPER will always be suppressed by the filter. (This is assumed that the frequency during the debounce period never exceeds 500 kHz (as required by the Nyquist theorem when using a 1 MHz sample frequency). The LED will always be ON when the debounce filters are enabled, as the inputs in this case will be sampled continuously. 4454_140 v1.0 167 |
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