Learn TWO ways to remotely access the PLC that is built-in to the GS4 Variable Frequency Drive. It's easy when you know how!
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There are two ways you can communicate with the GS4 Variable Frequency Drive’s built in PLC. The first way is using ModBus RTU. The Drive and PLC have different ModBus addresses, so you can simply configure your controller to talk to the two different addresses via the drives Modbus port. BUT, that’s the hard way. Because even though you are really talking to the GS4 Drive in both cases, now you have two ModBus addresses you have to manage in your controller. And if you accidentally write data to the drive when you meant to write data to the PLC you can really mess things up. If you do choose to use this method, please keep in mind that the GS4 Drive’s PLC is a ModBus slave only. Which means it can only respond to queries from an RTU Master. And, you can only access the PLC via ModBus RTU. You can’t access it via the optional Ethernet/IP or ModBus TCP communications cards. The good news is the GS4 Drive has a much easier and safer way for your controller to transfer data to and from the GS4 drives built in PLC and you CAN use ModBus RTU, ModBus TCP or Ethernet/IP to do it! Each GS4 Drive has a set of 20 parameters that the PLC can use for whatever it wants. The PLC simply issues a read parameter or write parameter instruction just like it would for any other parameter. Maybe we have the PLC read the special function register which is analog input 1, and write that to parameter eight dot twenty, which is the first PLC buffer register. This number here is 814 hex, so that’s eight dot 14 hex. Which is 8.20 decimal. And here we are reading Parameter 8 dot 21, which is the second of the twenty buffer registers available. Well, since YOUR remote controller can access these drive parameters from ModBus RTU, ModBus TCP or EtherNet/IP it can read the PLC’s results directly from those registers OR put things in the registers for the internal PLC to read. Easy – right? The beauty of this is now your external controller only has to manage one ModBus device – the Drive – which makes your life so much easier. The PLC is now just a co-processor that adds functionality to the drive – which is all it was meant to be in the first place. And look at this … since each of these buffer registers is just a Drive Parameter you can see what’s in each register right on the keypad. So, this gives you a quick way to see what the PLC is doing which makes debugging communications with your remote controller super easy. You can see what the remote controller is sending to the internal PLC and what the internal PLC is sending to the remote controller. How cool is that? So, while there are two ways to communicate with the GS4 Drive’s internal PLC, doing it via the built-in registers is definitely the better way to do it. Click here for more information on the GS4 Drives. Click here to learn about AutomationDirect’s free support options. Click here to subscribe to AutomationDirect’s YouTube Channel so you will be notified when we publish new videos.