Manual

8-6 Using the Digital Outputs and Inputs
Responding In Mid-move
The MN ("Mid-move Digital Inputs Response") command can set up automatic Digital
Inputs responses that occur while the carriage or the Z motor is in motion. The System can
"remember" where it was when the Digital Inputs reached a particular state and can
immediately decelerate and come to a stop.
This capability is especially useful where there is a piece of external equipment monitoring
some quantity which is affected by the Automove System's motion. (For a laser trimming
example see the MN command in Chapter 3.)
To prevent unexpected results you should be sure that the MN features are only enabled
during the particular move or group of moves where you desire a response.
Timing Considerations
You must design your ACL move sequence and your external hardware carefully to prevent
timing problems when using the Digital Inputs. In general, you must ensure that inputs
occur early enough, occur in the right order, and last long enough to be seen.
Suppose that in your application you wish to test the state of an Input and perform one action
if the Input is True or a different action if it is False. You decide to put two XI commands,
one following the other, the first testing for True, the second testing for False. When the
first XI executes the Input is True, so its action is performed. But meanwhile the Input goes
False. Then the second XI is encountered, and its action is performed as well! In cases like
this it is safest to use the <else id> parameter of the XI command, in order to guarantee that
only one of the two actions is performed.
Similarly, suppose you wish to perform some action only if several Inputs are all in the
correct states. Where possible, it is safest to test them all in the same XI command, rather
than testing some of them from within the Download Sequence invoked by the first XI.
Otherwise, the first one you test may change before you test the others.
If a transition requires an extremely prompt response you should arrange for your move
sequence to be waiting for the transition via a WN command. The delay between a
False-to-True transition which terminates the WN wait, and the beginning of the next ACL
command, can be well under a millisecond if the following command is a CD or TD, and
about 3 milliseconds for an MA or MR vector.
Interrupts and Other Methods
If you set up personality parameters 36 - 38 appropriately, a False-to-True transition on a
Digital Input will trigger a Download Sequence. If another Download Sequence was already
executing it will be interrupted; after the interrupting sequence is finished the original
sequence resumes where it left off. Interrupts can also be caused from the front panel, by
pushing the FAST/PAUSE, FAST/TEACH, or GO buttons.