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sparkotronic

Using multiple MSG blocks

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Hi, I'm still fighting my way through PLC5 and Ethernet coms. I'm having problems with one of the PLC's on my work network. It occasionally drops off RSlinx and we lose all coms to the processor, when this happens I can access the ENET side card through IE so I don't think it is a network problem. The PLC in question has about 40 MSG blocks which constantly trigger. I've read that this can cause issues with time outs ect. The ENET side care is also set to 10mps 1/2 duplex, I'm hoping to change this on our next maintenance day to auto neg as I've installed new 100mps cisco switches. I'm also hoping to add diagnostic files to the ENET cards as well to try and get more data. The logic below is a sample of how it is done. I've read that this is not a good practice as you should cascade them. I have tried this in a few different methods with little success. Could anyone shed some light on this issue? I have 15 PLC's on the network and all MSG's are triggered the same way. I've got a Rockwell Ethernet course booked for next year and an arms length of questions to ask ;-p Thanks in advance, Colin

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You need to define the maximum acceptable latency for each of the message data blocks and at the very least, add logic (or find it elsewhere) to manage the buffer status and errors. Add a cascading mechanism or time driven trigger to those that can tolerate delays according to the defined tolerances to improve results. Also, make use of alternate channels. the PLC-5 still has a healthy and powerful DH= channel or two that can be tapped for a scada, hmi or programming resource without burdening the sidecar. 40 messages with no interlocking or cascading mechanism might be fine until you go online and add more connections to the system...

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Does your 1785-ENET have an RJ45 type jack directly on the front, or an AUI connector and a transceiver ? The jack directly on the front (and probably a label saying "10/100") indicates that it's a Series C module and can handle Autonegotiation and 100 Mb/s Full Duplex operation. I like to use a self-resetting timer (or several) to trigger groups of MSG instructions to a particular target that then execute in sequence. There are a lot of ways to skin this particular cat. I agree that you also want to be sure to define a Status File for each communication channel; that will help you diagnose any noise or errors on the port.

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Thanks for your replies. Is there any chance you could post some code examples on how to cascade the MSG's? I have tried a few things with no success and the PLC in question is a site show stopper when it (or I make it) fails! On the duplex, am I right in saying that 1/2 duplex means that the side card can only read or write and full means it can do both at the same time? I changed the side card a few months ago to the RJ45 style but I didn't know about the settings. Would making this simple change make a big difference? The PLC also has other PLC's reading from and writing to it, the whole thing looks messy to my untrained eyes. Thanks in advance Edited by sparkotronic

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My random thoughts on this. 1. DOn't go auto negtiate switch to 100mb defined both at the sidecar and the assocaited switch. I've seen auto-negs suddenly decide to reneg in the middle of running normally. 2. The easiest cascade would be to use a free running timer set for say 3 seconds. XIO T4:0/DN TON T4:0 300 0.01 0 The every time the timer is done BSL a spare Binary Register. XIC T4:0/DN BSL B3:99. Setup so that on First Scan Mov 1 B3:99 Also if B3:99=0 move 1 B3:99 Then use XIC B3:99/# {where # is 1 thru 15} to trigger messages. You'll want a one shot after the XIC B3:99/# but it should work. You can split your 40 messages into 16 groups and trigger 2 or 3 at the same time in each group. Hope that's clear.

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