Translating Mega pin numbers

Sorry if this already has an answer on the forum - my searches have failed to find one.

I am building a weather station. Some instruments talk 1wire, some I2C, and some need an intermediary. I already have a Trinket as a I2C Slave dealing with a pressure sensor.

I have just bought a Mega 2560 which I want to use as a I2C Slave and to count tips on a rain gague, revolutions of an anemometer, read a lightmeter (day/night), and a moisture meter(wet/dry). Probably more as the project developes.

I have written code to do this and would like to test it.

My problem is where to plug the wires in.

The documentation talks about external interupts on pins 2, 3, 18, 19, 20, 21. I2C is on 20 1nd 21.

SDA is pin 20 in the Arduino Mega documentation. The pinpout web sites show some of the pins with names like SDA 20, other pins do not have such a name. All of the pins have a number, SDA 20 is 44. SDA is also PD1 and INT1 and SDA.

What is the pin number? Is there a list anywhere.

John Hadley

20/21 sda/scl are the numbers you connect to (43/44 are the physical pins on the chip)
google: "atmega2560 arduino pinout" (pictures)

A good visual look can be seen about half way done this page:

https://arduino-info.wikispaces.com/MegaQuickRef

Thanks for the replies.

The web page econjack points to has pin numbers for all the pins. I have printed it out for future referwnce.

Thanks.

johnhadl:
Thanks for the replies.

The web page econjack points to has pin numbers for all the pins. I have printed it out for future referwnce.

Thanks.

Why do you need to know the chip pin numbers ? The Arduino functions use the board pin numbers and they are printed on the board itself.

The pinout diagrams I was working from had chip pin numbers for all pins, but Arduino pin numbers for only some.