Within a word, from bit 0 to bit 15, Result: messages a and b are displayed at once – Rockwell Automation 2706-MB1 MESSAGEVIEW 421 SOFTWARE MANUAL User Manual
Page 61
4–13
Planning an Application
Publication 2706-817
Bit trigger priority
Bit triggered messages are not queued as value trigger messages are.
However, bit triggering does provide a way to prioritize messages. If
two or more bits are set at the same time, the terminal processes
them according to the following criteria:
1. Bit triggered messages are prioritized from Least Significant Bit
(LSB) to Most Significant Bit (MSB):
–
within a word, from Bit 0 to Bit 15
–
if more than one word is assigned to bit triggering, from
Word 0 to Word 63.
2. The terminal scans the area of memory assigned to bit triggering
in prioritized order, from LSB to MSB.
3. When the terminal detects a set bit, the message corresponding to
that bit is triggered. It is displayed or not, according to the
following rules:
if the Bit Trigger is:
and the Display Line:
then the message is:
set (1)
is available
displayed
set (1)
is occupied
not displayed
set (1)
becomes available
displayed
reset (0)
becomes available
not displayed
Example 1
Two messages are bit triggered at the same time. Assume all display
lines are available and the messages are assigned to different lines.
0
0
0
0
0
0
0
0
0
0
0
0
0
1
0
0
0
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
Message A Display Line 1
Bit 2 Word 0 set
Message B
Display Line 2
Bit 0 Word 1 set
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
1
0
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
Word 0
Word 1
Result: Messages A and B are displayed at once.