Reference Command

Character: W
Decimal: 87
Hexadecimal: 0x57

Note: This command is available only in RMC CPU firmware dated 20020620 or later.

The Reference (W) command places the axis in the reference state, and configures the position filter used while in this state. The reference state is defined as follows:

The Actual Position status field reflects the actual reading from the transducer, and the Target Position reflects the filtered position, after applying the Filter Time Constant, Reference Deadband, Velocity Limit, and Acceleration Limit parameters described below. Axes gearing to this reference axis should select to gear to the reference axis's Target Position to use the filtered position.
The drive output is in open loop. It can be changed normally using Open Loop (O) commands. When the Reference (W) command is issued, the axis will switch from closed to open loop, if necessary.
While in the reference state, all motion commands for this axis are disabled. For example, Go (G) and Relative Move (J) commands will generate an Invalid Command parameter error but otherwise be ignored.
To exit the reference state, you must issue a Set Parameters (P) command, which will place the axis back into closed loop, disable the position filter, and re-enable motion commands.

Analog inputs configured as Position Reference or Velocity Reference axes are always in the reference state. Therefore, the Set Parameters (P) command will not exit the reference state. These axes have axis parameters dedicated to the position filter parameters: Filter Time Constant, Velocity Limit, Acceleration Limit, and Reference Deadband. These parameters can be edited like any other axis parameter or set through the Reference (W) command.

The Reference (W) command parameters are defined as follows:

Command Parameter	Description
Mode	Rotational/Linear Mode Select: All bits of the Mode must be zero except for the Rotational bit. The Rotational bit can only be set on axes with Quadrature, SSI, or analog velocity feedback. When this bit is set, the positions are wrapped between the Retract Limit and the Extend Limit.
Acceleration	Acceleration Limit: This parameter limits the rate that the Target Velocity can change. It is specified in position units per second per millisecond. Notice that this limit is ignored if the Filter Time Constant (described below) is zero.
Deceleration	Reference Deadband: This parameter configures a deadband that is used to eliminate jitter in the Target Position when the input is at rest. The Target Position does not change until the Actual Position moves at least the number of position units specified by this parameter. This parameter is specified in position units. A value of 0 disables the deadband feature.
Speed	Velocity Limit: This parameter limits the rate that the Target Position can change. It is specified in position units per second. Notice that this limit is ignored if the Filter Time Constant (described below) is zero.
Command Value	Filter Time Constant: This parameter defines the time constant for the filter to apply to the input. This parameter is specified in milliseconds. The cut-off frequency for a filter in Hertz, given the time constant (t) in seconds is computed by 1/2pt. If this parameter is zero, then no filter is applied, and the Velocity Limit, Acceleration Limit, and Reference Deadband are not applied.

For a complete discussion on the reference mode and configuring the position filter including examples and diagrams, see Reference Axis Filtering.