Read characters from the device – Rockwell Automation Logix5000 Controllers ASCII Strings Programming Manual User Manual
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Chapter 1 Communicating with an ASCII device
1. In the Controller Organizer, right-click Strings and choose New String
Type.
2. In the Name box, type the name for the data type.
3. In the Maximum Characters box, type the maximum number of characters
that the string data type stores.
4. Click OK.
As a general rule, before you read the buffer, use an ACB or ABL instruction to
verify that the buffer contains the required characters.
•
An ARD or ARL instruction continues to read the buffer until the
instruction reads the required characters.
•
While an ARD or ARL instruction reads the buffer, no other ASCII Serial
Port instructions, except the ACL, can execute.
•
Verifying that the buffer contains the required characters prevents the ARD
or ARL from holding up the execution of other ASCII Serial Port
instructions while the input device sends its data.
For additional information on ASCII Serial Port instructions, se
In the following example, the device sends a fixed number of characters, such as a
bar code reader:
Example:
A bar code reader sends bar codes to the serial port (channel 0) of the controller. Each bar code contains 24 characters. To determine
when the controller receives a bar code, the ACB instruction continuously counts the characters in the buffer.
When the buffer contains at least 24 characters, the controller received a bar code. The ARD instruction moves the bar code to the
bag_bar_code tag.
Read characters from the
device
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Rockwell Automation Publication 1756-PM013D-EN-P - October 2014