Allen-Bradley A-B QUALITY DL20 Series User Manual page 160

Appendix G
Application Notes
PLC-2
Programming Examples
G–8
Rung 2
This is the rung that actually triggers the message. Setting input address
111:14 momentarily will initiate one complete sequence, displaying the
message with variable data. If the application requires the variables to be
continuously updated on the display, then, address 111:14 should be set
high continuously for that period of time.
Timer 031 determines the time between step changes. This time should
not be set lower than 70 milliseconds per step for AC output module
applications using a Parallel Input Converter (2706-NG1, -NG2,
Series A or B).
For DC output module applications the minimum timer value (031) is 20
milliseconds (002 in the example). The DL20 scan time should be near
the minimum value 4 and likewise the debounce time should be set near
its minimum, 1.
Rung 3
A free-running timer is used to create the data value being displayed.
Rung 4
This rung and rung 17 assure that both the high byte and low byte data
portion of the variable are both moved to the appropriate word in the
sequencer file at the same time. Otherwise, the timer value could change
between the time that the high byte and low byte are strobed to the DL20.
The GET instruction (address 030) is the same address used for the
sequencer instruction and contains the current "step number". The equal
instruction (address 034) could have been any available address and must
store a constant (2 in this case), so that rungs 5-16 will only be scanned
and updated once per sequencer cycle. Any step can be selected,
however, step 2 is the last step prior to the variable data being sent to the
DL20.
Rungs 5-12
Transfer the low byte data from timer 032 accumulative value to the
appropriate sequencer step (word 043).
Rungs 13-16
Transfer the high byte data from timer 032 accumulative value to the
appropriate sequencer step (word 041).
Rung 17
Marks the end of the zone to be controlled according to rung 4.