Low Power Application on SAM E54 Using Harmony v3 Peripheral Libraries: Step 3
Configure Analog-to-Digital Converter (ADC) Peripheral Library (PLIB)
Configure ADC Peripheral
Under the Available Components tab, expand Peripherals > ADC.
Select and double click on ADC1 to add the ADC1 module to the project graph.
Select the ADC1 Peripheral Library and configure it to sample and convert the light sensor input. The ADC is also configured to generate an interrupt (and thereby wake the CPU) when the ADC result is greater than a set Window Monitor Low Threshold value (3000 in this example).
- When the light sensor is not covered (light is falling on the sensor), the phototransistor is turned on. The ADC input is ~0 V and the ADC RESULT register is close to 0x000.
- When the light sensor is covered (light is not falling on the sensor), the phototransistor is turned off. The ADC input is ~3.3 V and the ADC RESULT register will be saturated (0xFFF).
- The ADC RESULT register is compared with the Window Lower Threshold (WINLT), which is set to 3000.
- When the light sensor is covered (ADC RESULT > WINLT), an ADC Window Monitor Interrupt is generated. This interrupt is used to bring the CPU out of Idle/Standby Sleep mode when you cover the light sensor.
- Select Prescaler: Peripheral clock divided by 2 divides the ADC input clock with the configured pre-scaler value and provides more sampling time (CLKADC = 1 MHz/2 = 500 kHz).
- Select Reference: VDDANA.
- Select Conversion Trigger: HW Event Trigger.
- Start Event Input: Enabled on Rising Edge.
- Select Positive Input: ADC AIN6 Pin (the light sensor is connected to AIN6 pin of ADC).
- Select Result Resolution: 12-bit result (ADC conversion value range from 0 to 4096).
- Open the Window Mode Configuration panel:
- Select Window Monitor mode: Result > WINLT. A Window Monitor Interrupt is generated when the ADC result is greater than the configured WINLT value.
- Window Upper Threshold: Sets the upper threshold of the window comparator. It is set to 0 as the ADC resolution is 12-bit.
- Window Lower Threshold: Sets the lower threshold of the window comparator. It is set to 3000. This means that the ADC Window Monitor Interrupt will be generated when the ADC result is greater than 3000. This value is decided based on the light sensor voltage when we cover the light sensor; it approximately generates 2.2 V. Hence, the threshold is set near to this voltage.
- Enable Window Monitor Interrupt: A Window Monitor Interrupt is generated when the ADC result is greater than the configured WINLT.
- Open the Sleep Mode Configuration panel:
- Enable Run During Standby.
- Enable On Demand Control.
Configure ADC Pin
In the MPLAB® Harmony Configurator (MHC), select the Pin Settings tab and then scroll-down to PORT pin PB04 in Pin ID column and configure this pin as ADC_AIN6.
Configure ADC Clock for Low-Power
In the MHC, select the Clock Easy View tab and configure the ADC Clock by opening the Peripheral Clock Configuration tab by clicking on the button in the Peripheral Clock Configuration.
Configure External Interrupt Controller (EIC) PLIB for Switch Button
In this step, the switch button will be configured as per the following USER_BUTTON design schematic on SAM E54 Xplained Ultra Evaluation Kit.
Configure EIC Pin
In the MHC, select the Pin Settings tab and then scroll down to 122 in the Pin Number column and configure the PORT pin PB31 as an external interrupt pin for switch functionality as shown below. Internal pull-up is enabled to avoid false edge detection as there is no external pull-up on the SAM E54 Xplained Pro Evaluation Kit.
Configure EIC Peripheral
Select the Project Graph tab.
Under the Available Components tab, expand Peripherals > EIC.
Select and double click on EIC to add the EIC module to the project.
Configure the EIC block to generate an interrupt every time the user presses the switch SW0 as shown below, and enable filter functionality to avoid electrical noise on switch pin.
Configure Event System (EVSYS) PLIB
The EVSYS is added by default to the project graph.
Launch the Event System Configuration window by clicking on Tools > Event System Configuration.
Once open, you will see following window on your screen:
Configure the EVSYS channel 0 on the Event System Manager window:
Add Event Sytem channel and user by clicking Add Channel and Add User buttons.
- Set the Real-Time Clock Compare 0 (RTC_CMP_0) event as the event generator. The event is configured to appear asynchronously and to run in Standby mode with the on-demand feature enabled.
- Set the ADC Start of Conversion (ADC_START) as the event user.