Count Unwind

Type:	Axis Parameter Register
RMC70 Address:	Fn:13, where n = 12 + the axis number
RMC150 Address:	Fn:13, where n = 24 + the axis number
System Tag:	_Axis[n].CntUnwind, where n is the axis number
How to Find:	Axes Parameters Pane, Setup tab: Primary Control Setup
Data Type:	DINT
Units:	pu
Range:	> 0
Default Value:	1024

Description

This parameter is used on rotary position axes together with the Position Unwind, Position Offset and Count Offset parameters to convert the transducer feedback Counts to an Actual Position.

The Count Unwind parameter defines the range of feedback Counts that maps to the Position Unwind. As the encoder rotates through the range of counts de fined by the Count Unwind, the Actual Position will go through the entire range of numbers specified by the Position Unwind.

For axes configured as Rotary Absolute, the Count Unwind parameter must be a power of 2, such as 1024, 8192, etc.

Example:
Consider an SSI Rotary Absolute encoder with 8192 counts per revolution. The user wants to set it up so that it goes from 0 to 360 on one revolution. To do this, the Count Unwind must be set to 8192, and the Position Unwind must be set to 360.

Valid Range

The valid range of the Count Unwind parameter is limited for certain feedback types.

SSI Feedback on Absolute Rotary Axes
The Count Unwind parameter must be less than or equal to 2N, where N is the SSI Data Bits. For example, for a 13-bit SSI encoder, the SSI Data Bits would be set to 13, and the maximum Count Unwind value would be 213, which is 8192.
Resolver Feedback on Absolute Rotary Axes
The maximum value of the Count Unwind parameter for resolver feedback is 65536.

Changing this Parameter

Because this parameter affects motion, the axis must be disabled or in Direct Output before writing to this parameter. The Enabled and Direct Output Status Bits indicate these states of the axis. When changing this parameter from RMCTools, the software will automatically do this for you. This may cause a halt on the axis, which is expected.