Running a picomotor

[labit]

I'm not sure how active this thread is, but I have exactly the same problem - except that I'm trying to do this from a Mac (ouch).  

The connection set-up is:

Max OSX USB > Serial (RS232 convertor)  (gives a 9-pin D-socket)

RS232 to RS485 convertor (gives an RJ45 socket)

Cable (former ethernet cable) to the 8753 driver.

My problem is that I can write in Labview and am OK with electronics, but have no experience with serial comms.  My RS232 is working fine (I can write data to it and, if I fit a loop-back plug, read the data back, so it's OK).  But I have no detectable output at my RS485 output.

Should I be able to see my data there?  Across which pins?  Or do I need some kind of null modem cable or something somewhere?

Arrgh!  Any help very much appreciated!

Paul

[Christopher_T.]

Hi Paul,

It sounds like the driver is working just fine. I'm interested in what the 485 converter is. You could try doing a loop back test with the 485 (which is not the same as the 232) and see if you get any signal.

Serial Loop back

http://zone.ni.com/devzone/cda/tut/p/id/3450 (ignore the hyperterminal stuff, just do the method of loop back but with the connections as specified in this document)

What converter are you using? (part numbers?)

Thank you!

[labit]

Hi Chris,

This sounds promising!  The convertor came with the instrument I'm trying to drive - it's a NewFocus part number 8722 (NewFocus are a division of Newport, I believe), and I couldn't find any information on it; it's just labelled with the part number and "RS232 Adapter"; it's an active device (ie, it has chips inside), but that's all I can tell.   The USB - to- RS232 converter is a Keyspan model USA-19HS ( newly purchased, and with the driver installed from the CD).

Re. the loopback test - sounds ideal, but the page you indicated doesn't give the pinouts for the RJ45 connector (8-pin; I'm just using a standard Ethernet cable, which is just a direct pin-for-pin connection with no crossovers etc).  However, I can find the pinouts somewhere else.  The main question is, do I need the "more advanced" option which allows flow control?

If I understand correctly, I need to connect:

TXD+ to RXD+

TXD- to RXD-

and, for the flow control option:

CTS+ to RTS+ and

CTS- to RTS-

Is that right? 

Thanks,

Paul

[labit]

p.s. if it's of any assistance, the manual covering the Picomotor controller (8753) is online at:

http://www.newport.com/images/webdocuments-en/images/15242.pdf

Thanks again,

Paul

[Christopher_T.]

Hi labit,

I would first try it without the flow control, and then again with the flow control. This is just to verify that the 485 converter is working.

Thanks!

[labit]

Hi Chris,

    Well, I tried with and without the flow control, and no luck with either (unless I have my pinouts wrong).

The Labview vi sets up the serial port (COM4) with 19200 BAUD, 8 data, no parity, 1 stop, flow control none, 20ms delay between writing and reading, and enable character termination = Off.  I've also tried a few variants on these settings - are these right?

Also, do I need to assert or unassert the RTS State at any point in the write/read cycle?

Sorry for these dumb question - I feel like a chimpanzee trying to drive a car!

Paul

[Christopher_T.]

Hi Paul,

Interesting, you might want to contact the manufacturer of the RS-232 to 485 converter. I'm not sure if they are doing something special or if there is a better way to validate that the converter is working properly. They also might be able to help you better with interfacing the motor with LabVIEW.

Thanks!

[labit]

Hi again Chris,

    Well, the only good news is that I found a program from the supplier which does drive the picomotors, so at least something is working!  I now need to learn about using DLLs under LabView - apparently the manufacturer provides DLLs, but this is a whole new field for me.  I'm also assuming that DLLs aren't portable from Windows to OSX, and that it's not going to be straightforward to port things across to OSX?

Cheers,

Paul

[Christopher_T.]

Hi Paul,

You won't be able to call the DLL in MacOSX which would force you to use VISA commands to write out from the serial port. There was a command set on the user manual that you posted earlier. (Look toward the section on Hyperterminal and page 57).

Thanks!

[labit]

Hi Chris,

    Hmmm - thought so.  If only the whole world were Mac....

I'm getting to grips with DLLs under Windows, at least, and I think I'll wait a while before delving into direct serial commands.  

Thanks again,and Happy New Year!

Paul