Frequentie controller problem.

[NIbke]

I have a hitachi L200 frequentie controller.
The L200 has an modbus output on RJ-45 connector.
I would like to control the L200 with a C++ program.
I bought a RS232/RS485 convertor to make the conversion between my PC and the modbus.But I'am unable to connect the L200 with my PC it just doesn't respond.It always gives me an read error amd write error. I'am using a modbuspoll program that I found on the net.

 

[itsmoked]

First use Hyper terminal (comes with windoz) to prove your hardware and cable works. Then work on the controller.

Keith Cress
Flamin Systems, Inc.- <

http://www.flaminsystems.com>

 

[NIbke]

It used hyper terminal to check my wire and that works.
I'am using a rs485/rs232 from patton.
I did a loopback test with that, with the hyperterminal.
And thatworked as well.
I also checked to modbus at the company where I bought it,
and the modbus works with an HMI.

 

[ozmosis]

check your cable. The RJ-45 uses pins 5(pos) and 6(neg) for Modbus rtu into the L200.
I guess you have the Hitachi L200 manual for communicating?

http://www.hitachi.us/supportingdocs/forbus/inverters/Support/L200_Instruction_NB660XA.pdf

 

[NIbke]

I have the manual and I'm sure the wires are correct.
I used the same cable with the HMI and that worked.
I'am using model 2089 from patton as a RS485/RS232 converter. But that has XMT+;XMT-;RCV+;RCV- as connections.
I tried to connect XMT+;RCV+ together and XMT-;RCV- together and then the positive to SP and the negative to SN.
But that didn't work either

 

[ozmosis]

do parameters A001=03, A002=03 and A076=02?
Going from a 4-wire to 2 wire may need 120ohm between TX+ and TX- to terminate.
I wonder if there is a parameter in the drive to determine if telegrams are being recieved. Not sure.
I'm no expert on Hitachi drives it's just that we test most drives here in our lab and I know we did look at the L200 and tested the Modbus RTU link a few years back (btw, it is RTU and not ASCII you are outputting?). It did work ok after we figured the pin connections.

 

[NIbke]

And do I need to connect the RCV+;XMT+ amd RCV-;XMT- still together?I'll have to try with the 120ohm resistor

I'am sure parameters A001;A002;A076 are set in a good way.
I use RTU. Here is the site from the program that I used

http://www.modbustools.com

 

[ozmosis]

usually it is a case of connecting TX+ to RX+ and TX- to RX-, however, it might be worth double checking. You don't want to short-circuit the comms input.

 

[LionelHutz]

Do you get a response from the drive at all? When you send it a request does it respond with an error message or do you get no response at all? Have you monitored the traffic to see what you get? Do you understand what a Modbus message should look like?

It could be the way the converter is being controlled. The 485 transmitter needs to be turned on and off at the right times. It seems that converter requires hardware control and your scanning program possibly isn't doing this. I've always had good luck with B&B Electronics converters and have used the 485SD9TB converter many times. It does automatic transmitter control so you don't have to worry about doing it yourself. I've also used Modscan from

http://www.win-tech.com

with good luck.

 

[Barry1961]

Just in case..........

OPE/485 dip switch is on 485

A001=03
A002=03

Barry1961

 

[NIbke]

I'am 100% sure that my settings are correct on the invertor site.
Thx for the reply anyway

 

[LionelHutz]

As I already asked; What is the error? Do you actually get a response from the drive? Have you actually looked at the link traffic?

If you keep insisting that everything is correct then we're naturally going to assume that everything is correct which means it must be working.

 

[NIbke]

At first I get a write error, all the rest are read errors.
I don't get any respons from the drive.
If I send a command with the test center from that program I see the command that I send in the traffic. But I don't get any respons from the drive back.
I think it must have something to do that the L200 only has 2 ouput(send/receive pos,neg) and the input to my convertor is 4 inputs (transmit pos/neg;receive pos/neg).

 

[jraef]

You have the register map from the drive to know which registers you are polling? Did you look specifically at the message format that the drive is expecting? Modbus or not, the drive will have it's own message format within the Modbus RTU cofines. If your read / write messages don't match exactly they will not work.

Eng-Tips: Help for your job, not for your homework Read faq731-376

 

[LionelHutz]

OK, you have used the Hitachi HMI software sucessfully with your cable. Now, Modbus Poll isn't working. I'd say it's very likely to be in the hardware flow control of Modbus Poll.

The converter says it will do RS422 or RS485 (2 or 4 wire). Usually, with this type of port, you connect the TX and RX connections together as you have done.

With RS485, you have to turn the transmitter of the sending device on to send the data and then back off to receive the response. As I posted before, I've used the B&B Electronics RS485 converters that have automatic transmitter control very successfully. On the other hand, I've had very mixed results with converters that require hardware transmitter control.