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Receive Serial Data from the
ASCII Device
The ASCII modules receive a number of characters and transmit them to the
EtherNet/IP adapter via:
•
I/O – poll, COS, or cyclic messages
•
Explicit message
The received character string is captured when:
•
The specific number of bytes defined (Receive Character Buffer Length)
is received, or
•
The defined End-of-String Terminator character is detected.
When either of these events occur, the ASCII modules store the received
message string into its internal buffer and then transmits (produce) it onto
Ethernet at the next appropriate opportunity.
Set Up the Receive Character Buffer Length
The Receive Character Buffer Length is the number of characters that the
ASCII modules can receive from your I/O device into its buffer at one time.
If the module receives more characters than the Receive Character Buffer
Length, it internally generates an overflow and forces the data into the ASCII
module transmit buffer to be sent to the adapter. The subsequent received
characters are then received into the buffer and are handled at the start of the
next incoming message string. The overflow bit in the status byte is set as well.
Incoming characters could be missed in the process of handling a string
IMPORTANT
longer than the
This value can be set and retrieved by using the standard set and get
services on Class 15 (F
Set Up and Use Pad Mode
Pad Mode operation adds extra characters to the end of its received data string
(after the delimiter character). These characters are added by the module to the
received characters from the external I/O device before sending to the
controller.
The quantity that is added is such that the data string that is returned to the
scanner is always a constant length, and that length is the number that is
specified in the maximum Receive Character Length parameter plus the 4-byte
header. The quantity of pad characters that are sent can vary from message to
message, depending upon the size of the incoming string.
Pad Mode Selection
Pad Mode allows for compatibility with scanners that cannot receive variable
length I/O messages. For such scanners, you must turn Pad mode ON (a value
of 1). Turning Pad mode ON does not harm Scanners that do support variable
length receive messages.
Rockwell Automation Publication 1734-UM009C-EN-P - August 2022
Chapter 3
defined max length.
), Instance 3, Attribute 1.
hex
Module Tag Definitions
27
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