Rockwell Automation 2706 DL40 HARDWARE USER MANUAL - Manual (Page 91)

Chapter 9
Using the Parallel Port
9 – 7
the [CTRL][W] in the second position would be sent in the low nibble of
the high byte of Variable 4. The low byte of the Variable 4 would be
ignored (unless the message contained more BCD variables).
In the Message List Run Mode, messages are continually being displayed by
the DL40. Messages can be added to or deleted from the message list while
the list is running. In addition,
Priority Message Numbers can be sent to
override the message list.
The 4 strobe lines specify an instruction to be performed.
MS3 MS2 MS1 MS0 Data Type
x x 0 0 null
x x 1 0
D0–D15 contain a message number to add
to list.
x x 0 1 D0–D9 contain the number of a Priority
Message.
x x 1 1 D0–D15 contain a message number to
delete from list.
x = Ignored
While the DL40 is in Run or Debug Mode, it regularly monitors the 20 lines
on the parallel port. Input data is only considered valid when all lines remain
unchanged for the time specified by
Data Hold Time in the Triggering Port
Setup.
You must insure that any data sent to the DL40 is held stable for at least as
long as the
Data Hold Time . If there are any switching delays on the lines,
data must be held for the length of the Data Hold Time plus delay time.
Since the DL40 has a feature which prevents a message number or variable
from being entered more than once, there is no problem holding data for
longer periods of time. When a DL40 reads the data at the parallel port, a
copy of the data is retained. If the next reading during the sample interval is
the same, the DL40 will ignore the second sampling, preventing the same
data from being sent to the queue more than once per scan. If you want to
re–trigger a message or variable, MS0–MS3 lines should be set too for a
minimum of 5 msec (plus switching delay time).
Message List Run Mode
Sampling