Dear friends in control!!

Can somebody help me to understand the explicit message mode of DeviceNet
control?
I have for tests the Allen Bradley PLC --> SLC 500 and devicenet module UD
77 for Control Techniques UNIDRIVE

Thanx in advance
Jacek

 

I have not used AB for this but have used Omron. The manual should tell you how to set up your read - class ID, instance ID, node number and service data. It is pretty daunting first time around but it works well when you finally get it set up properly.

 

Hi,

Commonly, a PLC interchanges data with Devicenet Devices through a Scanlist Memory in the Devicenet Scanner. This means you have to map every I/O you want to use in the scanner. The scanner polls the devices, the plc reads the scanner Memory...

The explicit messaging is quite different: The PLC sends a command to the scanner, the scanner process the command (sending or retrieving data to/from a device) and returns an answer. The command could be something like "Set Value" or "Get Value".

I guess you want to set the drive's speed setpoint: In the drive manual must be some information about the command you need to send to the scanner, like:
TRANS ID, CMD
PORT, SIZE
SERVICE CODE, MAC ID
OBJECT CLASS
INSTANCE
ATTRIBUTE ID

The trans Id is a number you give to the message to identify it (1 byte)
CMD is the command for the message (commonly 0x01, which means "Execute this trans block")
Port is the devicenet port of your scanner (in SLC must be 0x00)
Size is the size of the trans block in bytes (commonly 0x06 for set instructions, for get the size depends of the data which is retrieved).
Service Code is given in the Drive Manual (commonly, a get is 0x0E, a set is 0x10).
Mac Id is the Devicenet Node number of the Device
Object Class, Instance and Attribute ID are the identifiers of the specific parameter you want access to.

You may construct you command, put it in some integer files (N7:0 to N7:5, por example) and perform a Block Transfer write to your scanner.

You can get some examples at www.ab.com, in the knowledge base. I suggest you look for "Explicit Messaging" and "slc block transfer".

Best regards
Rafael Becerra
Project Engineer
Omnicon Ltda

 

Jacek,

I wnet through this nearly a year ago... Here is a link:

http://www.control.com/1026161263/index_html

To a message I posted then. Follow the links in that message, and the ones linked to in the first link from that one. I try to give some info and details.

It has been a while for me, but hopefully that will give you some background, and you can come back with some specific questions if you still have trouble.

--Joe Jansen