ProSoft Technology MVI56-GEC - Manual (Page 75)

MVI56-GEC ♦ ControlLogix Platform Reference
Generic ASCII Ethernet Communication Module User Manual
ProSoft Technology, Inc. Page 75 of 108
October 8, 2010
Multiple Blocks
If a server or client receives a message longer than 200 bytes, it must send the
received message in multiple blocks to the processor. In this case, the byte count
field of the block will be set to -1 for each block where the server is sending more
than 200 characters. Each block with a byte count field of -1 contains 200 bytes
of data. The data set is located in the block starting at word offset 2. When the
last block of data to send by the server is less than or equal to 200 bytes, the
byte count field will be set to a number from 1 to 200. This signifies to the
processor that this is the last block. The ladder logic must handle data received
on each server or client enabled in the module.
The module status data begins at word offset 102. Refer to Installing and
Configuring the Module for a full discussion of this data set. The ladder logic
should use the state value of each server to determine which servers have open
connections (state value of 1). Ladder logic can send messages to any open
connection.
Word 248 of the message informs the ladder logic of the number of bytes sent in
the last write block that were processed by a server. Ladder logic should check to
make sure all bytes sent to a server are processed. If not, data may be lost.
The last word of the input image (word offset 249) is the block sequence number.
This word’s value changes each time the module has processed the previous
output image or is sending new information to the processor. This value should
be copied to the first word of the output image (write block sequence number).
Both the processor and the module can easily recognize the arrival of new data
by the sequence number.