ADLINK Technology PCI-8254, User Manual

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152 Motion Control Theory
4.9 Motion Status Monitoring
During the motion control process it is necessary to monitor
motion status of control axis and convert to next process control at
appropriate time. Take example. During system initialization the
upper control program (the control program of user) execute home
operation to each control axis at first. The controller starts home
movement once the command is received and the control program
must wait for the completion of home operation. Usually the polling
method is used to determine the completion of homing process.
That is, read motion status signal of controller at regular time
span. Next stage control operation starts only after current
movement is completed.
In addition, there may be exceptional situations occurred during
motion operation. The upper control program must be able to
detect abnormality and deal with exceptions accordingly. Take
example. When emergency stop button is pressed during home
movement or the end limit signal is triggered during movement.
See figure below for basic flow chart of home movement.
Figure 4-56: Motion status monitoring process
Motion control status and its behavior provided by this controller
shall be described in Section 4.9.1.
Start home move
Polling home move
done?
Exception?
Next step control Error handling