![]() When this bootloader is ‘burned’ to a new Atmega2560 microcontroller using the ICSP, it essentially gains the ability to watch for and accept code uploads over another interface as well. This is accomplished via a bootloader, or a tiny program that controls the startup behavior of the firmware. ICSP is the ‘official’ way to upload code to the Atmega2560, so how does USB work? For this programmer, you would select AVR ISP.įrom there you can write and upload Arduino code to the board as normal, as long as the programmer is connected on one end to your PC and the other end to the Arduino ICSP header. ICSP is used by obtaining an external programmer like, and indicating in the Arduino IDE under Tools→Programmer what you are using. It is a lower-level way to upload code to an AVR microcontroller compared to USB. ICSP, or In-Circuit Serial Programming, is an SPI-style interface that requires an external programmer to upload code to the microcontroller. However, there is an alternate way to upload code to an Arduino board in the form of the 6-pin header labeled ‘ICSP’ on the dev board, with the same name in the schematic. If you are freshly coming from dev-board Arduino programming, you may now be wondering how to program the board if there is no USB port.Īfter all, with the development board you just plug the computer into the USB port and upload code that way. It also demands that a portion of the board edge must be clear for the USB port itself, which can be an issue in size-critical applications. It adds additional cost for the extra microcontroller and all of its required external components. The main argument against doing something like this is that if you are not using the USB functionality for something critical to your application (your device does not need to hook up to a PC for example), then including built-in USB connectivity is unnecessary. This brings us to a critical decision point in the hardware designing process whether or not to retain USB functionality on the new manufacturable design. The smaller one, the Atmega8U2-MU, plays the role of USB-to-serial conversion, since the Atmega2560 does not have built-in USB functionality, only UART.įigure 2 – Schematic diagram for Atmega8U2-MU USB-to-UART circuit The larger microcontroller is, of course, the Mega. When first looking at the schematic what will stand out is that there seems to be two microcontrollers, a larger one on the left and a smaller one on the right.įigure 1- Schematic diagram for Atmega2560 core microcontroller circuit When it comes to the rest of the schematic, there is generally no reason to not reference the schematics for the official Arduino development board. If your ADC requirements are not very strict, you can ignore this and simply tie the pin to a capacitor. ![]() This reference can and should be separate from the primary power supply, even if the voltages are the same. This is an IC designed to provide a very stable, noise-free DC voltage source that does not need to provide very much current. ![]() This can be left floating or shorted with a capacitor to ground, since the microcontroller can source its own reference.īut if your application has particularly stringent analog performance requirements it is recommended to use a dedicated voltage reference chip. Note that the microcontroller provides an AREF pin on pin 98 for the package above. It is a 5V microcontroller like the Uno, so your first step when transitioning this chip to a custom PCB should be to ensure that your board provides a 5V source to power the board. There are 54 standard GPIO available and a variety of peripherals including dedicated PWM channels, the typical serial interfaces like SPI and UART, and more. In the iteration that is found on the Mega board, the microcontroller comes in a standard TQFP 100-pin package. Starting with hardware, the Arduino Mega is based on the Atmega2560 microcontroller.
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