Rockwell Automation 1771-QA Stepper Positioning Assembly User Manual - Manual (Page 35)

3–13 Programming and Operation
Publication 1771-UM002A–EN–P – May 2000
Avoid sending multiple commands to the stepper controller module
at the same time. A programming error could result or the
data/command could be ignored.
All bits must be set carefully to tailor the move profile(s) to the
application requirements and to avoid illegal bit combinations. If
only one command is transferred at a time with proper handshaking,
no difficulty should be encountered. An illegal bit combination will
cause a programming error when data is received by the stepper
controller module or when move data is processed for execution.
Once the definitions of the bit functions have been learned, the table
of illegal bit combinations found in section titled “Illegal Bit
Combinations,” can be consulted as an aid in avoiding programming
errors when programming the required move profile(s).
Offset Word
The position offset allows an entire positioning profile (all moves of
the profile) to be shifted to compensate for machine wear without
reprogramming the profile (Figure 3.8). The offset value between 0
and 7,999 pulses, can be added to or subtracted from the final
position of each move in the moveset(s).
Figure 3.8
Offset
– +
Move 1
– +
Move 2
– +
Move 3
0
Rate
Position
Offset
10521
The offset value is entered in BCD in bits 00-16 of the offset word.
Bit 17 is the control bit that determines whether the offset will be
added to or subtracted from the final position (Figure 3.9). The
value entered in the figure is the maximum allowable value of offset.
Refer to offset command bit 13 of the moveset control word
described earlier in this section