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xAM - Axis Mode
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Sets the function of the axis.

    0 = Disable. All input to that axis will be ignored and the axis will not move.
    1 = Standard. Linear axes move in length units. Rotary axes move in degrees.
    2 = Inhibited. Axis values are taken into account when planning moves, but the axis will
        not move. Use this to perform a Z kill or to do a compute-only run.
    3 = Radius mode. (Rotary axes only) In radius mode gcode values are interpreted as linear
        units; either inches or mm depending on the prevailing G20/G21 setting. The conversion
        of linear units to degrees is accomplished using the radius setting for that axis. 
        See ARA for details.

 ZAM = 2       Inhibit the Z axis; $zam1 will restore standard operation
