Count Unwind

Type:	Axis Parameter Register
Address:	RMC75: %MDn.13, where n = 12 + the axis number RMC150: %MDn.13, where n = 24 + the axis number RMC200: %MDn.29, where n = 384 + 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.

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 and Values

The valid range and values 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. The Count Unwind parameter must also be a power of 2, such as 1024, 8192.
Resolver Feedback on Absolute Rotary Axes
The maximum value of the Count Unwind parameter for resolver feedback is 65536. The Count Unwind parameter must also be a power of 2, such as 1024, 8192.
EtherCAT Feedback on Absolute Rotary Axes

The Count Unwind value must evenly divide into the total encoder range. The total encoder range is the Encoder Wrap Maximum - Encoder Wrap Minimum + 1. The maximum value of the Count Unwind parameter for EtherCAT feedback is 2^31 - 1.

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.