Rockwell Automation 160-DN2 160-DN2 DeviceNet Communication Module FRN 3.xx - Manual (Page 65)

Publication 0160-5.18 - June 2003
Using 160-DN2 with DeviceNet Scanner 6-27
Using Explicit Messaging
(Continued) PLC-5 / SLC Explicit Message Requests
Word Description
0 Command (Least Significant Byte)
The Command is a code that instructs the scanner how to administer the request
during each download.
00 = Ignore transaction block (empty)
01 = Execute this transaction block
02 = Get status of transaction TXID
03 = Reset all client/server transactions
04 = Delete this transaction block (available only for SLC)
05 – 255 = Reserved
TXID (Most Significant Byte)
The Transaction ID is a 1-byte integer between 1 and 255. It is assigned in the
ladder logic program when the processor creates and downloads a request to the
scanner. The scanner uses it to track the transaction to completion. It returns this
value with the response that matches the request downloaded by the processor.
1 Size (Least Significant Byte)
The size of the service data is in bytes. Service data includes the words for the
class, instance, attribute, and any data. The maximum size is 58 bytes (29 words).
Port (Most Significant Byte)
The port that is used by the message is always zero (Channel A) on an SLC
scanner. It is zero (Channel A) or one (Channel B) for a PLC scanner.
2 Address (Least Significant Byte)
The node address of the slave device to which the transaction is sent. For the
Explicit Message to be successful, the slave device must be in the scanlist of the
scanner, and it must be online.
Service (Most Significant Byte)
Available services depend on the class and instance that you are using.
Refer to
Appendix B for available service.
3 Class
Refer to
Appendix B for available classes.
4 Instance
Refer to
Appendix B for available instances.
5 Attribute
Refer to
Appendix B for available attributes.
6 – 31 Request Data
This is data used for the message. For example, it may be the value written to a
parameter.