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  Chapter 6  Programming Motion 
DMC-2X00  
When a Galil controller is configured for step motor operation, the step pulse output by the controller 
is internally fed back to the auxiliary encoder register. For SPM the feedback encoder on the stepper 
will connect to the main encoder port.   Enabling the SPM mode on a controller with YS=1 executes an 
internal monitoring of the auxiliary and main encoder registers for that axis or axes.  Position error is 
then tracked in step pulses between these two registers (QS command). 
YC
YB
YA
TP
TD
QS
×
×
=
 
Where TD is the auxiliary encoder register(step pulses) and TP is the main encoder register(feedback 
encoder). Additionally, YA defines the step drive resolution where YA = 1 for full stepping or YA = 2 
for half stepping.  The full range of YA is up to YA = 9999 for microstepping drives. 
Error Limit 
The value of QS is internally monitored to determine if it exceeds a preset limit of three full motor 
steps.  Once the value of QS exceeds this limit, the controller then performs the following actions: 
1.  The motion is maintained or is stopped, depending on the setting of the OE command.  If OE=0 
the axis stays in motion, if OE=1 the axis is stopped. 
2.  YS is set to 2, which causes the automatic subroutine labeled #POSERR to be executed. 
Correction 
A correction move can be commanded by assigning the value of QS to the YR correction move 
command.  The correction move is issued only after the axis has been stopped.  After an error 
correction move has completed and QS is less than three full motor steps, the YS error status bit is 
automatically reset back to 1; indicating a cleared error.  
 
Example: SPM Mode Setup 
The following code demonstrates what is necessary to set up SPM mode for a full step drive, a half 
step drive, and a 1/64
th
 microstepping drive for an axis with a 1.8
o
 step motor and 4000 count/rev 
encoder.  Note the necessary difference is with the YA command. 
 
Full-Stepping Drive, X axis: 
 
#SETUP 
 
OE1; 
Set the profiler to stop axis upon error 
KS16; 
Set step smoothing 
MT-2; 
Motor type set to stepper 
YA1; 
Step resolution of the full-step drive 
YB200; 
Motor resolution (full steps per revolution) 
YC4000; 
Encoder resolution (counts per revolution) 
SHX; Enable 
axis 
WT50; 
Allow slight settle time 
YS1; 
Enable SPM mode