CTI 2572-A, Installation And Operation Manual

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CTI 2572-A Installation and Operation Guide V1.3 99
Uncoupled Mode Timing (CMD Mode =0)
Uncoupled Mode may be selected when close synchronization between the PLC and the module is
not required. In this mode, a single trigger can cause the module to execute a command many times.
Uncoupled mode is useful in applications where you want to continuously update the remote PLC.
Uncoupled Mode usually takes less PLC logic to implement than Coupled Mode. The following
figure illustrates the timing relationships between CMD TRIG and CMD BUSY for an Uncoupled
Mode command. The shaded area in the diagram indicates that it does not matter what the status of
the bit happens to be (
don't care condition).
At time A, the module has
cleared CMD BUSY,
indicating that Command
processing is complete. When
CMD BUSY is low and CMD
TRIG is high the module will
assert CMD BUSY (Time B)
and begin command
processing. CMD BUSY will
remain on during the
processing of the Command
Block. When the processing
is complete, the module will
lower CMD BUSY (Time C).
Note that in Coupled Mode,
the module would wait for the
PLC to lower the trigger
before clearing CMD BUSY
.
At the next end of the PLC
I/O scan, the module will again sample CMD TRIG. If CMD TRIG is high, the module will raise
CMD BUSY and execute the same command again, without re-reading the Command Block from the
PLC. Note that the PLC logic is not required to cycle CMD TRIG.
If continuous operation is desired, the PLC can simply leave the CMD TRIG on. The Module will
then repeat the command as fast as possible.
NOTE:
As long as the 2572-A detects that CMD TRIG is high when CMD BUSY is lowered, it will execute the
same command again, It will not re-read the Command Block from the PLC. Therefore, if you wish to
change the command to the module, the PLC logic should clear CMD TRIG and ensure CMD BUSY
is cleared before changing the contents of the Command Block or the associated Command Slot.
Alternately, use Coupled Mode for these applications.
Figure 14. Uncoupled Mode Timing