Bridging a bunch of DH-485 Micro's onto DH+


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John Kelley

We have a plant-wide DH+ net used for data collection (mostly, although there is some messaging between a few PLC-5's and a SLC 5/04) and I have added several 1000, 1200 and 1500 Micrologix linked seperately on a DH-485 net via NET-AIC+ modules. I need to get some data from a 1200 to the DH+ network. AB's web site suggests a "bridge" is possible between using a SLC 5/04 (connected to both the DH+ and serial ports -- The PLC 5's etc. on the DH+ side and the Micro's on the DH-485 to AIC+ side). However, their doc's say that, while a Micro can read msgs. from the DH+ net, it cannot initiate msgs. across the DH+ network. I know that I could (probably) use a AB bridge in a PLC-5 like a 1785-KA5 (PLC-5 card that allows communication passthru from the DH-485 thru a -5's DH+ connection) but it's expensive. Any other options or experiences would be appreciated. The 1200 Micro collects demand from a MAJOR load of 6.5 megawatts, and I want to broadcast it through the plant for consumption by other equipment as operator info only. Thanks, John Kelley

Eric M. Klintworth

John, Using a 5/04 as a bridge is probably the simplest way for you to go. Two notes on your second paragraph: first, the MicroLogix 1500 and 1200 can both initiate messages to a remote network; the MicroLogix 1000 is the one that can only respond. See at Chapter 21 of A-B publication 1762-RM001C-US-P. Second, even with a MicroLogix 1000, you could still get data to or from a DH+ node. The 1000 can only respond, but the message instruction it responds to can be a message write _or_ a message read. So a DH+ node would have to initiate any communication to a 1000, but it could read or write data (i.e., the MSG instruction would be in the DH+ node, not in the 1000). Hope that helps, Eric M. Klintworth, P.E. Sharp Technologies, Inc. Columbus, Ohio