Rockwell Automation 1771-QA Stepper Positioning Assembly User Manual - Manual (Page 42)

3–20 Programming and Operation
Publication 1771-UM002A–EN–P – May 2000
In the continuous mode, the decel value is not used in the move
profile except for the last move. However, the decel value has a
special purpose in the continuous mode: it allows a controlled decel
to 0Hz rate under two conditions:
1. If a system fault is detected, the move in progress will decel to a
0Hz rate (come to a stop) in the time defined by the decel value.
2. If a software stop command is received by the stepper controller
module, a controlled decel to a 0Hz rate will occur during the
move in progress. This will happen only if the
decel/instantaneous bit of the moveset control word is set.
Otherwise the stop will be instantaneous.
!
ATTENTION: Select a decel value for a controlled
stop that is compatible with the stepper motor and
system dynamics in order to avoid damage to the
equipment. Refer to section titled “Application
Considerations.”
Position
The position value defines the final position of any particular move.
It is the number of position pulses from a reference value such as the
beginning of the move profile. When the number of pulses defined
in the position words of a move block equals the number of pulses
sent from the pulse output expander module to the stepper translator,
that particular move is done.
The most significant digits of the position value are contained in the
MS position word, the least significant digits in the LS position
word. Use leading zeros when necessary.
Status Block
The status block is a data table file used to store position and
diagnostic information received from the stepper controller module.
The status block contains the following word storage for each pulse
output expander module (axis).
•
Status Word
•
Position Word