Help! Powerflex4m and RS485!

[Zingfrid]

Hi all.

I have Powerflex 4m, i read a manual and find out that it support Modbus RTU via RS485. I try to communicate with it, but I have no answer from it. I looked at d015 parametr and find out that it recive my data, but it doesn't answer anything. From the PC side i'm using Linux and libmodbus-2.0.3. I think wiring is correct, becouse it recive my data. I've checked every parametrs according to ProwerFlex manual.

Please, help what else can be? I need to do it very quickly, but i have never do it before.

Thank you in advance.

 

[bernie_carlton]

Assuming that the communication parameters set in the drive match those you are using then make sure that you cycle power. We have found that the address we use in when addressing is 1 more than that listed in the manual. For example the speed reference which is listed as 8193 we have to address at 8194 (which in MODBUS terms ends up being 48194).

I would advise at first just using the stated MODBUS addresses until that works well before trying to aaccess other drive parameters.

 

[Zingfrid]

What do you mean? "which in MODBUS terms ends up being 48194"? I've already try it. I've checked all addressed from 8100 to 8200... and have no repyly.

 

[bernie_carlton]

The addresses in MODBUS have an initial numeral denoting their function (input, output, holding register etc). This gets encoded into the message. When we use MODBUS from either and AB or from an AutomationDirect unit the raw address (eg 8194) gets modified byt the instruction parameter box according to our function. Typically 8194 gets changed to 48194 to denote that it is a holding register rather than an input/output etc.

If you are unfamiliar with MODBUS the get the manual at www.modbus.org. Go to 'tehnical resources' (on the left side) then 'MODBUS Specifications'. You will have to agree to the terms. Then you can download the specification which explains the memory layout.

 

[bernie_carlton]

I also confirmed with Allen Bradley that the MODBUS addresses for the standard parameters is stated incorrectly in the manual. Just use the numeric part of the parameter as the address (with a possible 1 offset as discussed in the previous post to this thread.)

 

[Zingfrid]

Thank you very much for your help! I get everything work! I've spend two days, for it. My problem was that powerflex 4m doesn't correctly work after communication error. I need just to turn it off and on again! So, if you do not recive a replyes from Powerflex, just try to reset it!