Communication Protocol with RS485 and Yokogawa UP55A

[K C]

Ok, when you are sure that your device is configured the rigth way and the command is properly formed I can only come back at the hardware link.

I would be nice if you can check the RS-485 line with a oscilloscope.

You stil didn't answer my question about the terminators.

Is there a 0V conenction on both sides ? If so can try to connect both ?

[m3rv89]

Hi KC, is been awhile. Appreciate all the comments above.

I do not have a osciloscope with me at the moment. 
I did nont connect any terminators because the wiring is really really short.

"Is there a 0V conenction on both sides?" Could you please explain what do you mean by that? 

[K C]

Hi,

Although it is very good possible that a short RS-485 interface with no terminators and no 0V connection will function OK. But when it is not OK you have to think about the things you left out.

The 0V is named 'SG' (Signal Ground) in the manual (ch.17) If both side share the same powersupply and there is no isolated interface you don't need the SG connection. But just to be sure connect it.

Some RS-485 transceivers IC's can behave strange when the levels are not OK. Terminators at both sides can help.

Can you measure the voltage between the A+ line and SG and also between B- line and SG ?

Kees

[m3rv89]

Hi Kees, 

Thank you for the explaintion. Sharing the same ground is important.

Now, I would like to focus on the rs485 wiring part. 
I am having difficulties on rs485 protocol. There is SDA,RDA,SDB,RDB. Which would be the A+ line and B+ line?

[K C]

Hi,

First to get it completely right: RS-485 is an interface not a protocol. A protocol is software. RS-485 is hardware.

First there was a four wire RS-422. This is a double balanced line interface. One line for Transmit (Tx) and one for receive (Rx). One Tx and 1 or more Rx. Long distance possible in full duplex (Rx and Tx simultaneously)

Most of the time Full-duplex is not needed so it is also possible to use one balanced line. This is RS-485. Because both Rx and TX use the same line the Transmitter must have an enable. It will free the line after transmission.

The signals have various names. It seems that every manufacturer try to come up with different naming.

When I see  SDA,RDA,SDB,RDB as you say. I read SendDataA,ReceiveDataA,SendDataB,ReceiveDataB This is a 4 wire (2 balanced lines) RS-422 interface.

The connection would be SDA to RDA and SDB to RDB and visa-versa. I also would say that the A line is the plus and the B line is the -. But as you can see in the Yokogawa manual it is not true for this device.

In RS-485 you have a A and a B line. Where (in my opinion and a lot of manufacturers) the A is the + line and the B is the - line. Simply connect A to A and B to B.

Because the manual says B is + and A is - I would try to reverse the connection at one side. That is also the reason why I asked to measure the voltages.

Kees

[turkeyspdr]

Hi folks,

Same issue here, only with a UT550.

Yokogawa has parameter setting software available for my model (and a different download for the UP55A I believe).  I've proved out my RS-485 adapter by uploading parameters from the controller.  Still not getting any feedback.

I downloaded some example programs for another different Yokogawa controller from the forums here:

http://forums.ni.com/t5/LabVIEW/yokogawa-UP150-driver/td-p/208434

The commands follow very similar nomenclature.

Have you had success talking to your UP55A yet or can we tackle this together?

Best regards,

Jeremy

[turkeyspdr]

Just found this post on the forums re: a different Yokogawa controller:

http://forums.ni.com/t5/Instrument-Control-GPIB-Serial/Communication-Protocol-with-RS485-and-Yokogaw...

Right click on your string control and change display from normal to "\ codes display".  See if you get any love.