I've connected my nowforever vfd with a USB->RS485 interface and I can write to it to change frequency (2301, 901HEX) but I get a error response. This is using modbus master poll software. In mach3 I can't get it working at all. It does however seem to be a problem with the response from the slave not returning properly.

I have programmed a PLC to set the frequency and read out a few parameters and that works flawless so it's some kind of issue with the computer/settings/interface I guess.

I don't know how to upload pictures to this forum but I hope I don't break any rules by posting a link to another forum where I have uploaded photos/logs/screenshot that explains the problem more in detail.

http://www.cnczone.com/forums/chinese-machines/275124-cnc-cad-software-forum-post1921498.html#post1921498

I'll reply to myself. I realized when looking through pictures that the  VFD and the PLC was grounded common and that I used only two wires for RS485 skipping ground wire. With the computer prolly not grounded that good since the PSU isn't grounded I guess it must have been some potential difference. Grounded the RS485 interface and communication was working.

Don't you wish all problems were this easy to solve?
Mike

So true Guess I ask to fast on a forum but sometimes you work so long with a thing that you get stuck looking at the wrong things/over complicating the problem. This was kinda the same thing. I've been working on it more or less the last 12hours not getting much progress. When I started going through pictures and making posts it got me looking at it from another perspective and it gave me a idea