Hello Robert,
I don't have experience on connecting FRDM with Arduino R3 board. But I know Erich ever wrote a set of articles on this related. Can you please check if this can be helpful to you:
https://mcuoneclipse.com/2012/09/28/kl25z-freedom-board-and-arduino-headers/
https://mcuoneclipse.com/2012/12/14/frdm-kl25z-with-the-arduino-motor-shield/
https://mcuoneclipse.com/2014/01/05/frdm-with-ardino-ethernet-shield-r3-part-1-sd-card/
Have a great day,
Jennie Zhang
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