Relay Ladder - Allen-Bradley Logix5000 Reference Manual

Chapter 17 ASCII Serial Port Instructions (ABL, ACB, ACL, AHL, ARD, ARL, AWA, AWT)
Arithmetic Status Flags:
Fault Conditions:
Condition
Prescan
Rung-condition-in is false
Rung-condition-in is true
EnableIn is set
Instruction execution
Postscan
temp_high
600
· In structured text, condition the instruction so that it executes only on a
transition.
3. Each time the instruction executes, do you always send the same number of
characters?
If
Yes
No
Not affected
None
Execution:
Relay Ladder Action
The rung-condition-out is set to false.
The rung-condition-out is set to false.
The instruction executes when rung-condition-in toggles
from cleared to set.
The rung-condition-out is set to true.
N/A
The instruction sends a specified number of characters and appends either one or two predefined characters.
The .EN bit is set.
The remaining status bits, except .UL, are cleared.
The instruction attempts to enter the ASCII queue.
The rung-condition-out is set to false.
Example 1:
When the temperature exceeds the high limit (temp_high is set), the AWA
instruction sends a message to a MessageView terminal that is connected to the
serial port of the controller. The message contains five characters from the DATA
member of the string[1] tag, which is a string. (The $14 counts as one character. It
is the hex code for the Ctrl-T character.) The instruction also sends (appends) the
characters defined in the controller properties. In this example, the AWA
instruction sends a carriage return ($0D), which marks the end of the message.

Relay Ladder

Rockwell Automation Publication 1756-RM003N-EN-P - October 2011
Then
In the Serial Port Control Length, enter the number of characters to send.
Before the instruction executes, set the LEN member of the Source tag to
the LEN member of the Serial Port Control tag.
Structured Text Action
No action taken.
N/A
N/A
EnableIn is always set.
The instruction executes.
No action taken.
AWA
ASCII Write Append
Channel
Source
SerialPort Control
SerialPort Control Length
Characters Sent
EN
0
string[1] DN
'$1425\1'
temp_high_write ER
5
6