Allen-Bradley A-B QUALITY DL20 Series User Manual page 163

Triggering Messages with Variable Data
This program example illustrates how a message with a variable data value
from a PLC-5 Programmable Controller can be displayed on a DL20.
There are 10 data lines (D0-D9) and 2 strobe lines MS0 and MS1 on the
DL20. If both MS0 and MS1 are high, it indicates to the DL20 that the value
present on the data lines D0-D9 is a message number to be triggered. At this
point, all 10 data lines (D0-D9) are examined. If binary message data is
selected, then the range is 1 to 1022. If BCD message data is selected, then
the range is 1 to 399.
The DL20 displays variable data from the programmable controller within a
range of 0 to 32, 767 binary or 0 to 9999 BCD. Because these are 16 bit
data values and the DL20 has only 10 data lines, each variable must be
strobed into the DL20 in two parts, 8 bits at a time. First the high byte is
strobed in. This is indicated by setting the strobe bit MS0 low and MS1
high. Next the low byte (least significant data) is strobed in to the DL20.
This is indicated by setting the strobe bit MS0 high and MS1 low.
When a message is created on the DL20 a variable data symbol
placed anywhere and up to twenty times within a message by pressing the
[Ctrl] key and [V] or [X] at the same time. For most keyboards (2706
keyboards) the [Ctrl] key and [V] or [X] must be pressed simultaneously.
For the 1770-T3 Industrial Terminal, they must be pressed sequentially.
Control V is for non-decimal point variables and control X is for decimal
point variables and or fixed format variables. The programmable controller
must sequentially strobe the variables into the DL20 data queue in the same
order that the variables appear in the message. After the variables are
queued, the message number is triggered.
The following program example uses a sequencer output instruction from the
PLC-5 to strobe the information into the DL20 parallel port.
Appendix G
Application Notes
or can be
G–11