Rockwell Automation 1771-QA Stepper Positioning Assembly User Manual - Manual (Page 37)

3–15 Programming and Operation
Publication 1771-UM002A–EN–P – May 2000
Initialization Preset
Typically it may be necessary to jog the machine to a starting
position before the positioning profile(s) is (are) started. The
position register of the stepper controller module will read some
number of position pulses representing the machine starting position.
The initialization preset can be used to reset the value of the position
register to zero, or to any value that would be used as the profile
starting value.
If the preset value were not set equal to zero (or not equal to the
profile starting value), when started, the first move(s) of the profile
would be shortened or lengthened. The amount would be the
difference between the initialization preset and the starting point
value: shortened if the preset exceeded the starting point value or
lengthened if the value were less than the starting point value
(Figure 3.10).
!
ATTENTION: All moves must achieve a final rate
for a minimum duration of 20ms or a programming
error and a system fault will result. The minimum
duration of a move is covered in section titled
“Application Considerations.”
Figure 3.10
Initialization Preset and Starting Value
Preset > Starting Value
Preset = Starting Value
Preset < Starting Value
Initialization Preset
Move 1
Final rate must be mainained for 20ms, minimum
10523
Rate
Position
1
1
Bit 17 of the MS preset word is the assert bit for the initialization
preset. When this bit is set, the preset value will be written over
whatever value is in the position register of the stepper controller
module. Once the positioning profile has been started, bit 17 must
not be set or a programming error will occur.