600 Rockwell Automation Publication 1756-RM003N-EN-P - October 2011
Chapter 17 ASCII Serial Port Instructions (ABL, ACB, ACL, AHL, ARD, ARL, AWA, AWT)
· 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?
Arithmetic Status Flags: Not affected
Fault Conditions: None
Execution:
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
If Then
Yes In the Serial Port Control Length, enter the number of characters to send.
No Before the instruction executes, set the LEN member of the Source tag to
the LEN member of the Serial Port Control tag.
Condition Relay Ladder Action Structured Text Action
Prescan The rung-condition-out is set to false. No action taken.
Rung-condition-in is false The rung-condition-out is set to false. N/A
Rung-condition-in is true The instruction executes when rung-condition-in toggles
from cleared to set.
The rung-condition-out is set to true.
N/A
EnableIn is set N/A EnableIn is always set.
The instruction executes.
Instruction execution 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.
Postscan The rung-condition-out is set to false. No action taken.
temp_high
EN
DN
ER
ASCII Write Append
Channel 0
Source string[1]
'$1425\1'
SerialPort Control temp_high_write
SerialPort Control Length 5
Characters Sent 6
AWA
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