The buttons pins are the same as on the 1286 Topboard, pins D23,D24,D25. Please see the pinouts maps in our documentation section for all pin definitions: https://static.industruino.com/downloads/diagrams/Industruino_INDIO_D21G_pinout_map_April'17_S.pdf & https://static.industruino.com/downloads/diagrams/Industruino_PROTO_D21G_pinout_map_April'17_S.pdf
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