ATmega2560 Barebones without Bootloader

Using Arduino Microcontrollers
1

Hi All,

I'm looking to add an ATmega2560 directly to my board layout after just about finalizing my program on the Arduino 2560. Since info is scarce on barebone 2560s, specifically, I wanted to ask for any insight on how to do so. The functionality of my project includes the use of about 10 I/O pins total, two of which are SPI MOSI & SCLK, and two of which are I2C SCL & SDA, and for testing purposes, the ability to read the main Serial line would be beneficial. So specifically:

  1. What external electronics are needed for a barebone ATmega2560? So far I believe all that is needed is an oscillator w/ capacitors, 100nF capacitor between power and ground, and pull up resistors for the I2C pins. I also will be adding the same power supply from the Arduino to the board, unless someone has a better option. For programming, I'm assuming I need a header in which I'll connect my external programmer, but am unsure of exactly what pins need to be used for the 2560 specifically.

  2. What programmers could do such external programming with no bootloader? I read that some programmers that work with the mega8 and mega168, for example, dont work for the 2560.

Any help is appreciated, thanks in advance!

Pat

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  1. Need access to Reset, SCK, MOSI, MISO, Power, Gnd for the programmer. Connect them to standard ICSP header:
    MISO 1 2 Power
    SCK 3 4 MOSI
    Reset 5 6 Gnd

Barebones: 10K reset pullup, 0.1uF/100nF on Every VCC/AVCC pin, and also Aref.
I2C pullups. That's about it.

Adding FTDI type header for debugging is good:
DTR, Tx, Rx, Power, Gnd, Gnd. (check the order)

I use Atmel AVR ISP MKii for my programming.
I recently developed a card to allow programming from a file on SD card. Nick Gammon modified has program to run on it.
http://www.crossroadsfencing.com/BobuinoRev17/
htt://www.gammon.com.au/forum/?id=11638

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3

As Crossroads said, you just need a bunch of 0.1uF caps and a 10K pullup on the reset line, plus a crystal + caps or resonator if you don't use the internal clock. Same as with a 328. I don't bother with I2C pullups, but I also don't use I2C at this point.

An ISP programmer and access to the 6 pins detailed by Crossroads are all you need if you are willing to program via ISP. Otherwise you can burn the bootloader and upload over Serial (in which case you need those pins broken out, and a 0.1uF DTR cap is handy). There are Arduino-compatible bootloaders for the 640, 1280, and 2560, which are all the same chip just with different amounts of flash mem (64K, 128K, and 256K respectively).

Check out Sparkfun's Mega Pro Mini, the schematic is effectively a barebones (leave off any LEDs and accompanying resistors that you don't want). I found it handy when building some Atmega640 boards a few months back. https://www.sparkfun.com/products/10743