microchip-pic-avr-examples/avr128db48-getting-started-with-xoschf-mplab

These MPLAB X bare metal examples in Getting Started with High Frequency Crystal Oscillator (XOSCHF) in AVR® DB (TB3272), show how the XOSCHF and Clock Failure Detection (CFD) is used on the AVR DB family of microcontrollers.

Getting Started with External High-Frequency Oscillator on AVR® DB MCUs

The High Frequency Crystal Oscillator (XOSCHF) enables the use of an external crystal or an external clock signal up to 32 MHz. This can be used as a clock source for the Main Clock (CLK_MAIN), the Real-Time Counter (RTC) and the 12-Bit Timer/Counter Type D (TCDn).

The Clock Failure Detection (CFD) feature can be used to detect if the output from a clock source stops and can switch the Main Clock to a different clock source to continue operation or shut down operation safely.

These examples show the following use cases for XOSCHF and CFD on AVR® DB MCUs:

• XOSCHF with External Crystal: Initialize XOSCHF for external crystal and change the main clock source to XOSCHF
• XOSCHF with External Clock: Initialize XOSCHF for external clock signal and change the main clock source to XOSCHF
• RTC with XOSCHF: Use XOSCHF as clock source for the RTC
• TCD with XOSCHF: Use XOSCHF as clock source for TCD0
• TCD with XOSCHF and PLL: Initialize the PLL with XOSCHF as clock source and use the PLL as clock source for TCD0
• CFD on XOSCHF: Initialize the CFD to monitor XOSCHF, enable the interrupt, toggle an LED if the clock source fails
• CFD on Main Clock with NMI: Initialize the CFD to monitor Main Clock with XOSCHF as clock source, enable the interrupt as a Non-Maskable Interrupt (NMI), toggle an LED with frequency derived from Main Clock

Related Documentation

• TB3272 - Getting Started with External High-Frequency Oscillator on AVR DB
• AVR128DB48 Device Page
• AVR128DB48 Curiosity Nano User Guide

Software Used

• MPLAB® X IDE 5.40 or later
• MPLAB® XC8 2.20 or later
• MPLAB® X AVR-Dx_DFP version 1.4.75 or later
• For the Atmel Studio version of these projects, please go to this repository

Hardware Used

• AVR128DB48 Curiosity Nano
• Optional external clock source

Setup

The AVR128DB48 Curiosity Nano comes with a 16 MHz crystal soldered on. This can be used for most of the example projects, except for the external clock and RTC examples.

• XOSCHF with External Clock:
  • Disconnect the crystal by cutting the two straps on the top side of the board next to the crystal (J215, J216)
  • Connect the I/O lines to the edge connector by placing solder blobs on the circular solder points marked PA0 and PA1 on the bottom side of the board (J213, J214)
  • Connect a clock source to PA0 on the edge connector
• RTC with XOSCHF: Replace the 16 MHz crystal with one running at maximum 1/4 of the CLK_MAIN frequency

Operation

• Connect the AVR128DB48 Curiosity Nano to a computer using a USB cable
• Clone the repository or download the zip to get the source code
• Open the project folder you want to run with MPLAB X
• Compile and run the code

Conclusion

After going through these examples you should have a better understanding of how to set up different use cases for the XOSCHF on AVR DB family microcontrollers.