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am interfacing EM-18 rfid reader to raspberry pi 3 through USB. The data has being rotating left by one bit, each time when I read the data

closed as unclear what you're asking by Aurora0001, Milliways, Dmitry Grigoryev, Patrick Cook, Steve Robillard May 8 '18 at 5:48

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    DO NOT post images post text – Milliways Apr 27 '18 at 8:28

The data.read(12) always reads exactly 12 bytes from the serial interface - if the sent card id is longer or shorter it will mess up the next read.

If its always off by one on the next read, you probably need 13 bytes here - but it would be more robust to read until a certain character (eg. \n newline)

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