RS232 Communication with Daisy Chain

[bcaire]

I am having trouble communicating with two mass flow controllers that are connected in a daisy chain configuration.  I am able to give them each an address (simply 111 and 222) by connecting them individually.  I set and confirmed the address change in the Basic Serial Write and Read program.  However, when I connect the controllers in a daisy chain (which I believe is the preferred connection scheme) and send the command @@@254CA?;FF, the output is garbled and various error messages appear (BFFF0015, BFFF006B - Framing Error)

I need to be able to send different commands to each controller separately.  Any help would be greatly appreciated.

Thanks!

Ben

[bcaire]

I mistakenly wrote that I am using a RS-232 interface, when I am actually using a RS-485 interface.  The mass flow controllers are MKS 1179A's. 

Ben

[JÞB]

Ben, Did you remove the termination jumpers from all but the futhest down-stream device?

[bcaire]

I don't think the MKS 1179A's have termination jumpers.  

[AnalogKid2DigitalMan]

Aren't you supposed to include the address of the device in the command so the intended device knows that the command is for it to process?

-AK2DM

[bcaire]

That's true for individual commands, but the @@@254CA?;FF command should return all the devices and their addresses.  You may have a point though.  Should I just ignore these errors and write the code for each controller with the addresses given and see if it works?  I figured that wouldn't work unless these errors went away.

[AnalogKid2DigitalMan]

Yes, I'd try a command addressed to just one of the controllers first.

-AK2DM

[JÞB]

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@bcaire wrote:

I don't think the MKS 1179A's have termination jumpers.  

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RTM- they do.  so, did you double terminate the bus?

[bcaire]

Setting a termination jumper sounds very logical to me, but I can't find anything in the manuals that discusses the topic.  I think that I do not have to do that.

I have written code that calls on the different addresses and it seems to work fairly well.  I can send individual commands and the controllers respond accordingly. 

However, now I'm seeing that the serial port is resetting itself about every 20 sec.  This is also affecting the temperature data that is coming through the same serial port.  Seems like a code error now. 

Thanks!

Ben