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MPLAB® Harmony v3 Peripheral Libraries on SAMC2x: Step 2

Last modified by Microchip on 2023/11/09 09:08

Configure I2C, USART, and RTC Peripheral Libraries

Configure RTC Peripheral Library

From the bottom left tab, Available Components, expand Peripherals > RTC. Double-click, or drag and drop, RTC to add the RTC peripheral library (PLIB) to the project graph.

Configure RTC Peripheral Library​​

The RTC clock is set to run at 1 kHz internal ultra-low-power clock.

When a module is added to the project graph, MHC automatically enables the clock to the module. The default RTC clock source is an internal 1 kHz ultra-low-power clock (OSCULP1K).

​RTC clock set to run at 1 kHz internal ultra-low-power clock​​

Note: On the SAMC21N device, RTC can be clocked through several low power clock sources of 1 kHz and 32 kHz as shown above. The 1 kHz clock source retained (OSCULP1K) is enough to generate time periods of 500 milliseconds, 1 second, 2 seconds, and 4 seconds.

Go back to the project graph and configure the RTC PLIB to generate a compare interrupt every 500 milliseconds.

​RTC Interrupt Selection in Peripheral Library​​

Note: The Compare Value is set as 0x200. This compare value generates an RTC compare interrupt every 500 milliseconds

  • RTC clock = 1024 Hz
  • RTC Prescaler = 1
  • Required Interrupt rate = 500 ms

Hence, Compare Value = (500/1000) x 1024 = 512 (0x200).

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Configure I²C Peripheral Library and I²C pins

The Available Components tab, expand Peripherals > SERCOM. Double-click on SERCOM5 to add the SERCOM instance 5 to the project.

Configure I²C in Harmony 3

Select the SERCOM5 peripheral library and configure it for I²C protocol as shown.

Note: The SERCOM5 (as I²C) retains the default 100 kHz speed because the temperature sensor chip on I/O1 Xplained Pro Extension Kit can operate at 100 kHz I²C speed.

 The Pin Configuration tabs by clicking MHC > Tools > Pin Configuration.

Pin Configuration Tab in Harmony 3

The MHC Pin Settings tab and sort the entries by Port names as shown in the accompanying image. 

MHC Pin Settings

Now, select the MHC Pin Table tab and then scroll down to the SERCOM5 module as shown in the accompanying image.

  • Enable I²C Clock (TWI_SCL) on PB17 (Pin #65)
  • Enable I²C Data (TWI_SDA) on PB16 (Pin #64)

​MHC Pin Table

Note: This completes the configuration of the I²C peripheral library. The application code will use the I²C PLIB APIs to read temperature from the temperature sensor.

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Configure USART Peripheral Library and USART pins

In the Available Components tab, expand Peripheral > SERCOM. Double-click on SERCOM4 to add the SERCOM instance 4 to the project.

USART Peripheral Configuration in MHC

Select the SERCOM4 peripheral library in the Project Graph and configure it for USART protocol as shown in the accompanying image.

SERCOM4 Peripheral Library

Verify the default baud rate is set to 115200 Hz.

Note: The application will use the SERCOM4 (as USART) PLIB for printing messages on the serial terminal. Hence, only the transmit functionality is enabled and the receive functionality is disabled.

Go to the Pin Table tab and then scroll down to the SERCOM4 module as shown in the accompanying image.

Enable USART_TX on PB10 (Pin #30).

​MHC Pin Table

Note: In the SERCOM4 (as USART) configuration, USART is enabled for TX functionality and no USART Rx functionality is enabled.

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Configure DMA Peripheral Library

DMA Configurator by going to the MHC tab in MPLAB® X IDE and then selecting Tools > DMA Configuration.

MHC DMA Configurator

On the DMA Settings tab, configure DMA Channel 0 to transfer the application buffer to the USART TX register. The DMA transfers one byte from the user buffer to the USART transmit buffer on each trigger.

Based on the trigger source, the DMA channel configuration is automatically set by MHC.

  • Trigger Action: Action taken by DMA on receiving a trigger.
    • One beat transfer: Generally used during a memory-to-peripheral or peripheral-to-memory transfer.
    • One block transfer: Generally used during the memory-to-memory transfer on a software trigger.
  • Source Address Mode, Destination Address Mode: Select whether to increment the Source/Destination Address after every transfer. Automatically set by MHC based on the trigger type. For example:
    • If the trigger source is USART transmit, then the Source Address is incremented, and the Destination Address is fixed.
    • If the trigger source is USART receive, then the Source Address is fixed, and the Destination Address is incremented.
  • Beat Size: Size of one beat. The default value is 8 bits. For example:
    • If the SPI peripheral is configured for 16-bit/32-bit mode, then the beat size must be set to 16-bits/32-bits respectively.

MHC DMA Settings

Under the Project Graph tab, click on the SERCOM4 block.

In the Configuration Options, uncheck the Enable Interrupts option.
MHC Configuration Options

Note: In this lab, SERCOM4 (as USART) interrupt is disabled as the application does not need a callback on USART transfer complete. A USART transmit buffer empty event triggers DMA to transfer one byte of data from source (user buffer) to destination (USART Tx register). When all the requested bytes are transmitted, DMA PLIB notifies the application by calling the registered DMA callback event handler.

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