Dh+

Gabriel577

Member
G
Join Date
Apr 2003
Location
Ontario
Posts
11
I'm using DH+ tocommunicate between two SLC504, but I get a communication error when i disconnect from the plc that i'm online with. The error is from the other plc. Do you have any ideas??
 
Define:'error' as used in your original post.

What does the error say?
Where is the error displayed?

Define:'disconnect' as used in your original post.

Disconnect the DH+ physical connection (cable) from the PC or PLC?
Disconnect meaning "Go offline"?
 
I'm getting a communication error in one of the message instructions. The error is EB - Target node cannot respond because target node denies access.

I'm online at station 1. As soon as i go offline (with DH+ still connected) i get this error.
 
What node is SLC1, SLC2, and your PC?

Is this a new project or has it been running up until now?

How many MSG's are there?

Are they read or write or both?
 
This is a new project.
I'm online with SLC1

write SLC1 to SLC2
write SLC2 to SLC1
read SLC1 from SLC2

write SLC1 to SLC2
read SLC2 from SLC1
write SLC1 to SLC2
 
I am assuming that all node addresses are different for each device, and all are correct in the MSG's. Are you triggering the MSG's 1 at a time, or how are you triggering them?

When you are online and all MSG's are working correctly are you getting the correct data from that MSG?

Is it possible for you to zip the .rss's and attach it to a post here?
 
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All the nodes are setup proprely, the plcs are sending messages back and forth properly while i'm online. Only one message instruction is being triggered at a time. As soon as i go offline the error comes up.
 
Sounds like a job for.....

Terminating Resistors.

I had something similar happen recently. I was online via DH+ (PCMK card) with a SLC, while the electricians were installing the HMI. I stayed online to ensure everything was working fine.

When I got offline (hardware as well as software), the HMI could no longer communicate with the SLC. Fortunately, I had a pair of terminiating resistors on hand (former Boy Scout), and with those, communication was restored.

In my case, the PCMK was acting like a terminating resistor. It doesn't make sense that remaining connected hardware-wise but not software-wise would cause the trouble, but you still might want to give that a try.
 
What firmware rev is each processor?

I asked around and there was a problem with 2 node DH+ networks in at least 1 firmware revision series C frn 5 possibly erlier. This problem was fixed series C frn 6.

Most everyone I have talked to have no idea what that error message is!
 
I go back online and check if the PLCs are still communicating. They aren't so i check the error given by the msg instruction.
 
This may be a shot in the dark but how far apart (cable feet) are the two processors? I had some funny things happen on DH+ in the past when I was trying to test messaging between two processors with too short of a cable. It was some time ago but if I remember correctly the minimum distance of a DH+ network as recommended by AB is 10 feet.

grs
 
Now I am really starting to stab in the dark. Make sure that the data table file of the destination of the msg insructions are not "protected".



From RSLogix 500 help:

(For SLC 5/03, 5/04 and 5/05 processors)
Check Constant if you want values in the data table file protected from all changes via communication ports or your ladder program. Check Static to protect data table values from being altered by communication channels. Changes are only allowed by the ladder program during program execution. Check Mem Mod to apply the indicated protection to the memory module. To change the protection for existing files, access the Data File Properties dialog.

RSLogix 500 - Copyright Rockwell Software 2000, 2001, 2002

datatable2.gif
 
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