I am attempting to use a prototype shield (same one used for the UNO) on a Zero.
My problem is that my sketch uses I2C and the SDA/SCL pins on the Zero (and UNO) are not carried through to the shield. When using a UNO , this does not present a problem as A4 and A5 can be used instead but, with the Zero, as far as I can tell, there are no equivalent pins, neither A4/A5 or other.
Is there some way to configure the Zero AI or digital pins to serve as SDA/SCL??
A link to your shield might be needed. This one has SDA/SCL.
Thanks for the info camsysca. My shield IIRC is an Elegoo knockoff similar to this Adafruit:
Note it says "Every pin is brought out.." but it looks like the SDA/SCL space is taken up by an LED as is the case with mine. They do have a newer version that includes SDA/SCL but I would like to use what I have on hand if possible.
Arduino Zero: Arduino Zero — Arduino Official Store
The I2C pins are indeed only at those pins next to AREF. That means that your prototype shield is not compatible with an Arduino Zero.
The ATSAMD21G18 has "Sercom" devices which are internal versatile hardware devices.
The Arduino Zero has only one I2C bus and Sercom3 is used for that, as you can read here: https://github.com/arduino/ArduinoCore-samd/blob/master/variants/arduino_zero/variant.h#L150
You might use another Sercom device to create a second I2C bus on other pins:
TwoWire myWire(&sercom2, 4, 3); // This is not enough, more code is needed
But we see problems on this forum as soon as someone goes outside the normal Arduino code.
It is easier to buy a compatible prototype shield.
How good are your soldering skills? You might be able to extend it that way.
Thanks for the suggestions. Wound up just removing the proto shield LED and surrounding PCB above the SDA/SCL connectors on the Zero - can plug directly into them now. 
Also tried looking into the myWire option as Koepel suggested, using code found on another site, but found a couple of issues. First was it was not compatible with the Adafruit OLED library (maybe it could have been made to but such is beyond my pay scale).
Second issue, but only peripherally related, was that adding the associated Wire.h include to the program resulted in a "not found" compile error message. WTH??
This was using IDE 2.3.2 which I have been trying out for a week or so with mixed success. Couldn't figure out what the problem was so, tried same code in 1.8 and it compiled. Went back to 2.3 and tried an example I2C sketch (i2c_scanner.ino), which also has the Wire include, and it compiled. I have read on this forum of folks having sketches that compile on 1.8 but will not on 2.X so maybe this is more of the same. 
Anyhow, all's well now m/l and my proto shield is now compatible with both the Uno and Zero....
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