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2. Add 7 zeros to the end of your message.

3. Write your CRC-7 polynomial underneath the message so that the LSB of your polynomial is directly below

the LSB of your message.

4. If the LSB of your CRC-7 is aligned under a 1, XOR the CRC-7 with the message to get a new message; if

the LSB of your CRC-7 is aligned under a 0, do nothing.

5. Shift your CRC-7 right one bit. If all 8 bits of your CRC-7 polynomial still line up underneath message bits,

go back to step 4.

6. What’s left of your message is now your CRC-7 result (transmit these seven bits as your CRC byte when

talking to the jrk with CRC enabled).

If you have never encountered CRCs before, this probably sounds a lot more complicated than it really is. The

following example shows that the CRC-7 calculation is not that difficult. For the example, we will use a two-byte

sequence: 0x83, 0x01.

Steps 1 & 2 (write as binary, add 7 zeros to the end of the message):

CRC-7 Polynomial = [1 0 0 0 1 0 0 1]

message = [1 1 0 0 0 0 0 1] [1 0 0 0 0 0 0 0] 0 0 0 0 0 0 0

Steps 3, 4, & 5:

_______________________________________________

1 0 0 0 1 0 0 1 ) 1 1 0 0 0 0 0 1 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0

XOR 1 0 0 0 1 0 0 1 | | | | | | | | | | | | | | |

--------------- | | | | | | | | | | | | | | |

1 0 0 1 0 0 0 1 | | | | | | | | | | | | | |

_______________ | | | | | | | | | | | | | |

1 1 0 0 0 0 0 0 | | | | | | | | | | |

1 0 0 0 1 0 0 1 | | | | | | | | | | |

_______________ | | | | | | | | | | |

1 0 0 1 0 0 1 0 | | | | | | | | | |

1 0 0 0 1 0 0 1 | | | | | | | | | |

_______________ | | | | | | | | | |

1 1 0 1 1 0 0 0 | | | | | | |

1 0 0 0 1 0 0 1 | | | | | | |

_______________ | | | | | | |

1 0 1 0 0 0 1 0 | | | | | |

1 0 0 0 1 0 0 1 | | | | | |

_______________ | | | | | |

1 0 1 0 1 1 0 0 | | | |

1 0 0 0 1 0 0 1 | | | |

_______________ | | | |

1 0 0 1 0 1 0 0 | |

1 0 0 0 1 0 0 1 | |

_______________ | |

1 1 1 0 1 0 0 = 0x17

So the full command packet we would send with CRC enabled is: 0x83, 0x01, 0x17.

4.e. Motor Control Commands

The jrk has several serial commands for turning the motor on and off and setting the target. These commands are

mainly intended to be used in serial input mode, but they can be used in any input mode to turn the motor on or off

from a computer.

Motor Off

Compact protocol: 0xFF

Pololu protocol: 0xAA, device number, 0x7F

4. Using the Serial Interface Page 30 of 44