Communicating with MKS MFC

[jpods]

Hi,

I have a 1179A MKS MFC with RS-485 serial connection. I am trying to control this MFC through labview. I have a NI PCIe-8431/8, 8 Port, RS485/RS422 Serial Interface that I trying to communicate through. The MFC uses an RJ-11 cable for its digital RS485 communication. There is ground, D+, and D- pins that I have isolated coming out of the RJ11 and have a converter for a DB9 connector. I have tried a number of different pin connections in an attempt to communicate with the MFC all of which do not seem to work, mostly focusing on combination's of connecting the D+ to RXD+ or TXD+ and the D- to RXD- or TXD-. Using VISA I try to send a command to the MFC and I read what appears to be totally random responses. Not sure what I am doing wrong but MKS does not seem willing to provide much support so any help would be great! There is the correct power going to the MFC as well. Thanks

Jacob

[John_M.]

Hi Jacob,

The first thing I would recommend is trying to perform a serial loopback test. This will allow you to write some string out from the card and read it back. If this is successful, you can at least know that the card is performing correctly.

Then, take a look at the Serial Quick Reference Guide. This guide outlines the pin connections which map the RJ-11 connector to the DB9 connector.

Best Regards,

John M

[mschroer]

Hi Jake,

I actually have some RS485 MFCs from MKS that I communicate to with Labview.  Once you get it working, you'll be happy;  they are much nicer units than the analog MFCs.

I think the problem your having is the MFCs are designed for 2-wire RS485, and your RS485 card, or converter is a 4 wire device.  You'll need to short some of the signals from your RS485 converter together.  Your will need to wire together TXD+ and RXD+ to Data+ on the MFC.  TXD- and RXD- will connect to Data-.

Another hitch is that your RS485 converter will need a specific feature.  I think it gets called various things, but on my cards it is called "Auto-RTS" or "Auto-Toggle".  Basically, since there aren't separate receive and transmit lines with a 2-wire network, you can run into situations where both the computer and your MFC are trying to talk at the same time.  "Auto-RTS"  makes the computer 'release' the voltage on the communication lines when its trying to listen for a response, so the MFC can be heard.  If you don't have this, there are ways of fudging it in software... but I had mixed results with this in the past.

I can vouch for the linked RS485 PCI cards, because I'm using one to communicate to my MFC's right now!

http://www.quatech.com/pdf/universalpci.pdf

Good luck!

-Michael