15.4 ADC Noise Reduction Mode

When the SM[2:0] bits are written to '001', the SLEEP instruction makes the MCU enter ADC Noise Reduction mode, stopping the CPU but allowing the ADC, the external interrupts, the 2-wire Serial Interface address watch, Timer/Counter(1), and the Watchdog to continue operating (if enabled). This sleep mode basically halts clkI/O, clkCPU, and clkFLASH, while allowing the other clocks to run.

This improves the noise environment for the ADC, enabling higher resolution measurements. If the ADC is enabled, a conversion starts automatically when this mode is entered. Apart from the ADC Conversion Complete interrupt, only these events can wake up the MCU from ADC Noise Reduction mode:
  • External Reset
  • Watchdog System Reset
  • Watchdog Interrupt
  • Brown-out Reset
  • 2-wire Serial Interface address match
  • Timer/Counter interrupt
  • SPM/EEPROM ready interrupt
  • External level interrupt on INT
  • Pin change interrupt
Note: 1. Timer/Counter will only keep running in asynchronous mode.