27+ Arduino Mega 2560 I2C Pins
Pics. It has 54 digital input/output pins (of which 14 can be used as pwm outputs), 16 analog inputs, 4 uarts (hardware serial ports), a 16 mhz crystal oscillator, a usb connection, a power jack, an icsp header. Although i can still use them with port manipulation, i would like to manually add them to pins_arduino.h so i can accomplish a better manipulation using arrays.
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They are circled on the photo below, and marked gnd on the board. Assuming we use pins 8 and pin 9 for rx and tx on both arduinos, connect pin 8 on one arduino with pin 9 on the other one, and pin 9 on the first arduino to pin 8 on the second one. I've built my own pcb with atmega2560 in it.
By mistake, i've assembled some inputs and outputs on pins that arduino don't use.
As majenko says in his answer you must use a resistor in series with any led you connect, or you will damage both the led and the processor. I've built my own pcb with atmega2560 in it. I changed manually the code in enc28j60.cpp at lines 247 to use these pins, but if i change the cs pin (spi_ss) to another, like 49, because i have the sd card modul. By mistake, i've assembled some inputs and outputs on pins that arduino don't use.
