Rockwell Automation 1734-485ASC POINT I/O ASCII User Manual - Manual (Page 41)

Publication 1734-UM009B-EN-P - July 2003
Configuring Your ASCII Module 2-15
POINT I/O Parameters Receiving Serial Data from the ASCII Device
The ASCII modules receive a number of characters and transmits these
to the DeviceNet master 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 will then transmit
(produce) it onto DeviceNet at the next appropriate opportunity.
Setting 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. The length of the data string sent to the DeviceNet master is
less than or equal to this size, plus the 4-byte header.
If the module receives more characters than this number, it will
internally generate an overflow and force the data into the ASCII
module DeviceNet transmit buffer to be sent to the master.
The subsequent received characters will then be received into the
buffer and handled at the start of the next incoming message string.
The overflow bit in the status byte will be set as well.
IMPORTANT
Incoming characters could be missed in the process
of handling a string longer than the
defined max
length.
This value can be set and retrieved by using the
standard set and get services on class 15 (F
hex
),
instance 3, attribute 1.