DH+ Net Decoder & Oscilloscope Paterns

[andy_1983]

Hi,


We've been doing a lot of work to get our DH+ networks back as they should be, following years of poorly executed modifications.


We've been using Netdecoder, and Picoscope PC based oscilloscopes as part of this process.


I've read a lot of documentation about fault finding DH+, and how it works. I've found some good info on this forum, as well as on the Rockwell Knowledgebase. It's all been very useful.


Perhaps I'm going too far with this now - border line obsessed, but I want to decode the oscilloscope trace. What I cant understand is why it doesn't resemble the Netdecoder packets.


I've added an attachment with the first trend out of the scope on power up of the PLC (the PLC is just sat on my desk, and not connected to a network). also, the first packet logged in net decoder (taken at the same time as the scope) is shown.


There's no similarity at all... Even if you think there might be some preamble bytes. I'd have thought the net decoder software would just be picking up the same signal as the scope.


Has anyone else done anything like this with more success? I was kind of expecting to change the binary to ASCII and then start seeing some DLE/STX.....DLE/ETX etc.




Or is this somehow recoded in the U2DHP box and I'm wasting my time?!




Thanks for any help...


Andy

 

[Mike_RH]

30 plus years ago I did this, memory is very fuzzy. The data is manchester encoded, so you need an external decoder.

 

[andy_1983]

30 plus years ago I did this, memory is very fuzzy. The data is manchester encoded, so you need an external decoder.

Hi Mike,

The scope has a decoding feature, which is what the third trace is on the screen shot. Looking at it, it does seem to have done it reasonably accurately. The issue is I can’t seem to see any correlation on anything that comes out of it between the netdecoder protocol analyser and the Manchester signal picked up on the scope.

Andy

 

[AlfredoQuintero]

I am not so knowledgeable of the DH+ protocol, hence I can't give you precise advice. But I do know from my job at a previous employer that one of the best DH+ troubleshooting tools available about 20 years ago was the 5136-SD-ISA board from a Canadian company called S-S Technologies, which was purchased by Woodhead Industries in 1999, which was purchased by Molex in 2006. This is an ISA board, so you will need an old PC with DOS. The board is still available in eBay and even Molex has some links to its documentation. If your DH+ systems are still significant, it may be worth setting up an 5136-SD-ISA with the S-S Technologies utilities. I remember some customers praising the diagnostics capability of this board.
https://www.deutsch.molex.com/webdocs/mysst/pub/drivers/sd/sdisaman.pdf