Alison

Hi guys. First up, I have gone through all the MODBUS vids (thanks) and used the examples, but there are a few things I don't understand. I'm really sorry to ask, because I know these are simple things for you all, but I don't know where else to find this info... there is no one else I can ask. I have this V350 which is my "master" and a heat pump which is Modbus enabled, that I am trying to read data from, which would be the Slave. I have no means of programming anything on this heat pump; I cannot download a program to it, so I cannot put the Modbus Slave demo program on it (do I have to do this?! I mean how do you handle that, with stuff that isn't a PLC? Do they default to being "Slave" anyway?). I have some info for it that tells me the default address for the heat pump is 9, and that the COM setup is defaulted to 9600, 8, E, 1 (although I may be able to change this if I have to). I can upload the modbus "map" I have for the heatpump if it helps? So I used the example Modbus Master program given in the videos and I have changed the settings in the COM INIT function block accordingly. I would like to read the heat pump's setpoint temperature, then display it on the HMI. According to the info I have the heat pump uses holding register 0x24 for this value. I'm assuming this is a hex value and I have to covert to decimal, which is (I think) 36? so I have entered "36" as the value for the start vector in the MODBUS RHR fb. The length of that vector is (for now) just 1, as I am only reading this one register. I have also set the slave ID to 9 here too. The demo program takes the value from that register, and plonks it into MI5 on the Master. Well, nope. I can't get it to work. I am using the V350's RJ11 connection. It's only 2 wires for MODBUS although the connection on the heat pump has 3: A+, B-, and GND. I was just using A and B. If I can crack this little bit, I am pretty happy that I can do whatever else I need, it's just getting the basics - and teaching yourself something is never easy! What am I missing here? Is it that my physical connections are wrong, or is it programming..? Any advice is so welcome. I feel very stupid. Alison

Okay, bear with me here. I have a Vision 350 J T38. This has a USB micro port for programming (great, that works, yay, and I am happily plugging away through the basics of ladder logic, thank you for that!) It also has an RJ11 port, and RJ45 which is labelled EXP PORT. The VFD I want to talk to has a USB port(s). I have also got a USB/RS485 adaptor cable, which has 6 wires on - red, green, brown and black, plus orange and yellow. How do I get from the USB port on the VFD, to the RJ11 port on the PLC? I have some RJ11 phone cable but that only has four wires in. I am assuming the RJ45 port on the PLC is for extra I/O units only, or am I making an error here?

My 350 gave the same error (it had a program on already; I have *cough* liberated it from a piece of redundant equipment) and I followed the sticky topic here on bricked Vision units which did the trick.

Both units use Modbus RTU over serial which is a relief, I don't want to have to learn networking too!!

Hi all. I am brand new to all this, so please don't savage me too badly. I have a Vision 350 here, and I want to get it talking to two different Modbus machines - a heat pump and a variable speed motor drive. Initially I just want to poll the units from my Vision to find out stuff like speed of drive, or heat pump temp. I have modbus "maps" for both units so that helps! Eventually I'd like to use the Vision to control our entire pool set-up - I work for a swimming pool equipment wholesaler. This is really just me trying to teach myself something new, but getting more control over the VSD would be great (eventually). I've started off following the videos on Modbus and on PLC basics but I'm struggling with some things, just because I'm no programmer and this is all new to me. Could anyone please suggest some good starting points - tutorials, videos, further reading - that might help? For example I don't know why, as the first step in the Modbus vids, a system bit is used in the first net. I must have missed what this is/does somewhere - I feel like I have missed a set of videos inbetween the "What is a PLC/HMI" and "How to work Modbus" ones!! Thus far my understanding is that you make a pretty interface screen, tie the things you're doing on that screen to "nets" (which are basically steps in a program) and the Vision will follow the structure of the ladder from top to bottom. I *think* that the Vision (as Master) polls the Slave units, gets data from them from whichever modbus address I point it at, loads that data into its own memory and uses the data as variables that I've defined, then keeps on repeating that process. Am I anywhere near right, here? Thanks Alison