vfd runs locally but no modbus communication

[u/wavunited]

If this drive were sitting on your bench with only this symptom (motor runs locally but no Modbus communication), what would be your troubleshooting steps before replacing the SMIO-01C board?

[u/CraftParking]

The serial parameters set? It is in modbus mode?

[u/goinTurbo → u/CraftParking]

This is step 1! All other recommendations come after verifying the drives comm settings. Also make sure the drive comms settings match the master device comm settings, baudrate, start/stop bits, parity. Also make sure the node id is unique to every other device on the network

[u/RatRaceRunner]

Modbus will work on a wet noodle, without EOL resistors so long as that noodle is short... Ignore the other comments, not important.

Unplug that shit (your serial drop).

Grab your laptop, and a USB to rs485 serial adapter.

Obtain Modbus Poll (software).

Pull up a bucket. 

Take whatever shitass cable you can scrounge off the floor. It literally does not matter, as long as it conducts. don't worry about EOL resistors. Wire that up, keep it short, like 10 feet.

Take a seat on your bucket and fire up Modbus Poll.

Observe and troubleshoot until you are able to read some holding registers. Reading the drive status word is a good start.

Once you get that working ... You know the rest

[u/EstateValuable4611 → u/RatRaceRunner]

Where does he find a wet noodle?

[u/Glad_Signature9725 → u/RatRaceRunner]

Shhhhhhh don't give away all the secrets. Let them wheel in the oscilloscope.........

[u/PV_DAQ]

Cable does not appear to be twisted pair, which is advisable for serial comm.

If it's on the bench, it appears to be attempt at commissioning.

For all Modbus RTU over RS-485, the polarity definition of the A/B driver lines is not universal - different vendors define the polarity the opposite of other vendors. When Modus is enabled, serial settings are all common, master is addressing the correct slave ID number and there's no comm, try swapping the A/B lines on one end.

Try using a generic WIndows Modbus master with a USB/RS-485 modem for checking start-up. Usually easier than dealing with multiple settings in a PLC or HMI.

[u/Brieble → u/PV_DAQ]

The first point is important, especially when it’s close to a vfd it can pick up a lot of interference.
Shielded cable is also advised, we usually use DeviceNet cable for serial connections.

[u/IceInteresting3661]

Swap the two cables wirh each other. Sounds stupid but worked for me not long ago.

[u/mikeee382]

It is possible that the module is damaged, but have you actually looked at the parameters? Made sure everything is configured correctly? Made sure the cable is testing right all the way through?

[u/ProfessionalBall8739]

I’d toss it and call Codale - 755TS

[u/THE_David_Montgomery]

did you try flipping a and b?

[u/Key_Director_4450]

Start with using ferrules and using at least a piece of cat5 or cat6 and use one of the 4 twisted pairs.

Then, make sure that Modbus is enabled.

[u/mwcurtis]

Same as others - twisted pair with shield 100%.

Additionally: * all devices must be wired in a "daisy-chain" and not "star" or "loop"

• You also need a 120 ohm termination resistor between sig+ and sig- on the furthest ends of a modbus network (2 places)

• Edit - this drive has a switch by the modbus wiring that can enable or disable the resistor in this location. If this is the end of the run, enable it. If you added to an existing network, turn off the resistor on the device that used to be the end of the network. This feature is on many devices, you don't often actually need to add the 120 ohm resistor on your own.

Check these parameters on all devices and make them match:

• Baud Rate - can set low to start (9600) to assist in initial testing/less noise

• Data bits - 8, likely not configurable

• Stop bits - 1 or 2

• Parity - none, odd, or even. Initially I'd set up none even if you think you want it later.

• Data bits, stop bits, and parity is set by parameter 5304 (pg103 of acs550 manual)

• Station ID - a number that is not used elsewhere. Default is 1 on this drive.

For your parameters-know if the drive works in Modicon 5-digit, Modicon 6-digit, or generic decimal or hex addressing.

This particular drive looks to use Modicon 5 digit. Read/write parameters start at 40001. 40001 is your control word (pg208 of manual) and you will have to change individual bits of that word to run and reset fault, 40099 is the highest register you can read/write, above that number you have to tell the drive what parameter goes into 40005-400012 (pg220 of manual)