Parport to 7i92

Look at this on RS485.

www.go4b.com/usa/technical-support/produ...485-wiring-guide.pdf

You might need a common signal ground between the VFD and control PC.
Many converters connect only the two data wires and ground is somewhat assumed.

I have found it better to explicitly wire it.

My last 485 project was a Modbus master and three slaves, the network covered about fifteen hundred feet or 460 meters. Through a machine shop and heat treat facility. I used a Beldon twisted pair with shield and 120 ohm terminators at each end.
Controlling two Allen Bradley VFDs keeping them in sync.

Properly terminated noise should not be a problem. If you have a scope, put it on the lines and tell us what it looks like.

In t500-hotbus/rs485-wiring-guide.pdf from the link above I discover the requirement for wiring.
My wire is about 1m long, shielded, not twisted from my scrap box. It's not 120 ohms impedance. During my previous tests, I replaced it with a thicker one, add termination resistor, add and removed the GND link with no better result. I need to find a 120 ohms to be sure.

From the oscilloscope, it seems hy_vfd it trying to read ACV from the VFD every 600ms when no response: see HY_22Kw.jpg. The debug file shows that hy_vfd is picking up the noise as a response.

See HY_15Kw.jpg when my other HY is responding. Much more traffic.

Put your B probe on the bar TX line. Look at "A" TX and "B" bar TX to see transmitted noise.

Here is A and B

On the PCB, I located the rs845 transceiver chip : U4
Many rs485 transceiver have the same pinout as this one thvd8010.

Assuming this, it seems the query from the computer seems to be correctly decoded on the pin #1 : R (I didn't trace it yet, up to the MCU).
But I have level changes on pin #2 (Receiver enable, active low) neither on pin #3 (Driver enable, active high) or pin #4 (Driver data input)

Here are the signals on the 1.5kw for pins 1 to 4.

Here are the signals on the 2.2kw
DE signal (Driver enable, active high) remain low. Does it mean that the rs485 is not enabled !?

PS:
On June 5, I wrote thant I could execute some command on the VFD using SpindleTalker2. Today I couldn't succeed starting the spindle niether had a single response fron it. (I'm still using the shielded wire from my scrap box)

Try A channel on RS+ and B channel on RS- .
Lower right-hand side of control terminals.

They should mirror, and anything else is noise and should be rejected.