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_low
604
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.
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 reaches the low limit (temp_low is set), the AWT
instruction sends a message to the MessageView terminal that is connected to the
serial port of the controller. The message contains nine characters from the
DATA member of the string[2] tag, which is a string. (The $14 counts as one
character. It is the hex code for the Ctrl-T character.) The last character is a
carriage return ($r), 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, move 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.
AWT
ASCII Write
Channel
Source
SerialPort Control
SerialPort Control Length
Characters Sent
EN
0
string[2] DN
'$142224\01$r'
temp_low_write ER
9
9