DF1 Gurus Wanted

Does anyone out there in Forumland do a lot of telemetry work with Allen-Bradley's DF1 protocol ?

I have run into quite a few projects over the years where I've had consultants and integrators ask me "what's the best way to program my MSG instructions and configure my controllers ?" in a DF1 multi-node system, usually when there are radio modems involved. I have to turn them over to the Instruction Set Reference manuals and the SCADA Application Guide, and they usually grumble and set aside the books.

I have encountered even more startup descriptions of "I tried everything and then it worked", or worse, "I tried everything and it still doesn't work". I don't like these. I *really* don't like playing point-the-finger with the modem makers either.

So I'm looking for Forum members to share their best practices when dealing with things like report-by-exception messaging, or the DF1 Radio Modem protocol with multiple message initiators. I'm looking for diagnostic code and technique examples, and message management examples.

Mostly right now I'm looking for a show of hands: Who works with DF1 protocol extensively ?

Ken Roach said:

Does anyone out there in Forumland do a lot of telemetry work with Allen-Bradley's DF1 protocol ?

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We use DF1 as our standard serial protocol. We don't get involved in many radio modems yet, but we have customers that connect a couple motion controller over DF1.

So I'm looking for Forum members to share their best practices when dealing with things like report-by-exception messaging, or the DF1 Radio Modem protocol with multiple message initiators. I'm looking for diagnostic code and technique examples, and message management examples.

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DF1 with more than two nodes must be half duplex. If there are multiple message initiators then a token passing scheme must be added. I believe these features are available on DH-485. In any case DF1 half duplex will not work unless there is only ONE master so no node speaks unless spoken to.

You have got my interest though. I have customers that have systems in remote places and they/we use DF1. So far we have not run into the multiple initiator problem, but I know we would say don't used it.

Peter Nachtwey said:

We use DF1 as our standard serial protocol. We don't get involved in many radio modems yet, but we have customers that connect a couple motion controller over DF1.


DF1 with more than two nodes must be half duplex. If there are multiple message initiators then a token passing scheme must be added. I believe these features are available on DH-485. In any case DF1 half duplex will not work unless there is only ONE master so no node speaks unless spoken to.

You have got my interest though. I have customers that have systems in remote places and they/we use DF1. So far we have not run into the multiple initiator problem, but I know we would say don't used it.

Click to expand...

DH-485 does have a token hold/passing scheme (including retries).
The one problem I've always had with larger networks on DH-485 is the use of the AIC modules in conjunction with non-AB devices. The network would 'lock up'. I found that by increasing the 'token hold factor' this happened Less Frequently. But it would still occur. Increasing the hold factor has adverse affects on network speed.
The other thing is to minimize the number of nodes to just what's needed on the network. But it wasn't nearly as successful as adjusting the hold/retry factor.
Here's what AB says about DH-485
:::
Node Address

Enter a node address (from 0-31 decimal).

Protocol Control

Token Hold Factor

Enter the number of transmissions (plus retries) that a node holding a token can send onto the data link each time that it receives the token. Enter a value between 0-31. The default is 1.

Max. Node Address

Enter the maximum address that the initiator searches for before wrapping to zero. The default is 31.