Read Position

NI-Motion VI

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Read Position

Reads the position of an axis.

Device Compatibility

Device	Compatibility
7330	Y
7340	Y
7344	Y
7350	Y
7390	Y
NI SoftMotion Controller for CANopen—Accelnet	Y
NI SoftMotion Controller for CANopen—Xenus	Y

Board ID is a unique number assigned by Measurement & Automation Explorer (MAX) used to send and receive commands and data to or from a specific NI motion controller.

Axis is the axis to read.

Retn Vect indicates the destination for the return data generated by this VI. Available return vectors include return data to the host (0xFF), to a variable (0x01 through 0x78), to an indirect variable (0x81 through 0xF8), and do not return data (0). Refer to Input and Return Vectors for more detailed information.

error in (no error) describes error conditions that occur before this VI runs. The default input of this cluster is no error. If an error already occurred, this VI returns the value of error in in error out. The VI runs normally only if no incoming error exists. Otherwise, the VI passes the error in value to error out. The error in cluster contains the following parameters:

	status is TRUE if an error occurred before this VI was called, or FALSE if not. If status is TRUE, code is a nonzero error code. If status is FALSE, code is zero or a warning code.
	code is a number identifying an error or warning. If status is TRUE, code is a nonzero error code. If status is FALSE, code is zero or a warning code. Use the error handler VIs to look up the meaning of this code and display the corresponding error message.
	source is a string that indicates the origin of the error, if any. Typically, source is the name of the VI in which the error occurred.

Position is the axis position in quadrature counts (for servo axes) or steps (for stepper axes).

Bd ID Out is provided for flow control. You can string together NI-Motion VIs by wiring the Bd ID Out terminal of one VI to the Board ID terminal of the next VI.

Resource Output is the Axis, Vector Space, ADC, or Encoder you wired into the VI. Use Resource Output to pass the resource to another VI and/or to display information about the device.

error out contains error information. If error in indicates an error, error out contains the same error information. Otherwise, it describes the error status that this VI produces.

	status is TRUE if an error occurred, or FALSE if not. If status is TRUE, code is a nonzero error code. If status is FALSE, code is zero or a warning code.
	code is a number identifying an error or warning. If status is TRUE, code is a nonzero error code. If status is FALSE, code is zero or a warning code. Use the error handler VIs to look up the meaning of this code and display the corresponding error message.
	source is a string that indicates the origin of the error, if any. Typically, source is the name of the VI in which the error occurred.

Using This VI

The Read Position VI returns the instantaneous position of the specified axis. For servo axes, it returns the primary feedback position in counts. For open-loop stepper axes, it returns the number of steps generated. For closed-loop stepper axes, it converts the primary feedback position from counts to steps and then returns the value in steps. Closed-loop stepper axes require you to correctly load values of steps per revolution and counts per revolution to function correctly.

Note For closed-loop axes, this VI always returns the position of the primary feedback resource.

Tip Refer to the Read Vector Space Position VI for an easy way to read up to three axis positions for a vector space in one call.

Note Refer to VI Execution Times for benchmark timing information about your controller.

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