Comtrol UP DeviceMaster User Guide - Manual (Page 59)

DeviceMaster UP Modbus/TCP User Guide: 2000447 Rev. I Chapter 2. Programming Interface - 59
Receive Data Message
2.4.3. Receive Data Message
The Receive Data message format is similar to the format used in the Serial Port Data Transfer Object.
However, the data is in 16-bit integer format instead of byte format. The 16-bit integer format is required
when connecting to PLC-5 and SLC PLCs.
The following table displays the format of the Receive Data message.
Receive messages have the following characteristics:
• It returns all data in UINTs.
• The data length field indicates the number of valid bytes contained in the message.
• The message received from the PLC determines the actual length of the message returned to the PLC.
(This is often greater than the length of the actual Receive Data Message.)
• All unused bytes in a message returned to the PLC are filled with zeroes.
• The default order of the bytes is Least Significant Byte First. However, you can select the (PLC-5/SLC)
Rx MS Byte First option in the web page to return bytes by Most Significant Byte First. For more
information, see (PLC-5/SLC) Rx MS Byte First under
3.3.3. Serial Packet Identification on Page 69.
• The DeviceMaster UP supports serial packets of up 1518 bytes and socket packets up to 2048 bytes in the
Write-To-File and Write-to-File-Synced receive methods.
• For large received data packets:
- The data is automatically placed in sequential files.
- The files must be 256 integers in size with the exception of the last file. The last file may be shorter
than 256 integers as long as the total length of all files in the sequence is sufficient to hold the largest
receive packet, plus two integers for the sequence number and length parameters.
- All data has been transferred to the PLC when the sequence number is updated.
Name Data Type Data Value(s) Access Rule
Receive (DeviceMaster UP to PLC) message data
Read only
Structure of:
Produced data sequence
number
Data length (in bytes)
Data array
UINT
UINT
Array of UINT
0-65535 (FFFF hex)
0-222 (SLC) 0-248 (PLC-5)*
0-65535