POM no lights

[PLCGuy]

Trying to connect a Sure Servo to the BRX using the POM serial RJ12. I do not see any TX or RX lights. Should I see something even though comms is not working. I can not seem to communicate to the servo system through the POM.
I set the POM as master as per the servo manual. 19200 baud, 8 data bits, odd parity and 1 stop bit settings match the drive. But no TX or RX lights on POM. Using MRX starting at Modbus 40001 for 12 registers using #3 Read Holding Regs.

Seems even though my setting might be wrong, should I see some activity from the POM?

[PLCGuy]

What is Device Driver Error-@DriverError (ST143). I click on it and open IO but no error to be found.

[PLCGuy]

I switched over to a 485 cable and got at least one light to work. Too much pain, not using the Sure Servo. Will be sticking to the servo system I am presently using. That works great.

[BobO]

The driver error is just a very generic flag that signals that a box (like MRX) errored out.

And yes, at a minimum the transmit led should be blinking in response to the MRX/MWX.

What is the value of $InstalledPOM(DST50)?

Do you have any other POMs (like an ECOMLT or USB) you can try to make sure the POM port is happy?

[PLCGuy]

I changed over to rs435 both with the settings and cable and the tx light is solid. But still fails. I gave up trying to make the Sure Servo system to work. Hard wired I/O works and I can talk to the drive with the pc, but not the plc. Doesn't seem anyone else has tried this. i did not see any responses back from both the AD site and this site. There are no examples. Doesn't seem things get updated on various equipment. Most of the info in the manuals is for DL series PLC's. I do not think the Sure Servo supports Ethernet TCP/IP modbus. I was trying out the serial without any luck. I spent most of the day trying to make it work. I will just stick to the servo system I presently use now. It just works with all of AD's brand plcs.

I have the ethernet and usb pom and they work just fine. I doubt it is the POM. It makes it hard to trouble shoot when there is no specific error code. Within the the MRX i tried different settings but always get the green lights, so I really don't know if one of the settings is wrong when it is running.

I was just hoping someone else has used the Sure Servo on a Do-More. Maybe AD will see this and give it a whirl. Do a paper on it.

[franji1]

You might want to contact AD tech support.  They deal with these kinds of issue a lot, and know what to try.

I know RS-232 can have grounding issues - they can step you through all of that.

[BobO]

If the receive led isn't coming on, then the servo isn't answering.

There are definitely error codes being set. The System Status page in the System Information dialog dumps the messages. They are probably timeouts.

[PLCGuy]

yes they are timeout errors. Maybe I will call AD, hate to give up on this. Like to know why it doesn't work.

[PLCGuy]

Bobo just for your info, it is the Rx light that is on constantly. no blinking. I will call AD this morning.

[PLCGuy]

Okay, got it to work! Settings of course. Tech support walked me through it and now it works. Oddly enough what got me was in the MRX command it says "Modbus Address 4...+ Offset Value Entered Below". So I put 40001. I did not need the 4000, just the one. Funny thing I did earlier try it with just the 1 but other settings were incorrect making that not work. Apparently with all my dickering around I had figured out the settings but did not change the 40001 to just the 1.
Okay I feel stupid.

Then it turns out the firmware is old and I can not write to the drive. They did fix that in a newer firmware but when I asked if my firmware can be changed, I was told no. Really! I will go on their website and ask that question.

[BobO]

Good. I hate it when stuff doesn't work. Especially my stuff.

[PLCGuy]

of course like most Do-More processes, it was quite simple to do. What threw me off was the "Modbus Address 4...+ Offset Value Entered Below" Should that be re-worded?

[Mike Nash]

of course like most Do-More processes, it was quite simple to do. What threw me off was the "Modbus Address 4...+ Offset Value Entered Below" Should that be re-worded?

That would just confuse the other half of us instead. 

The hardest thing for me to figure out with Modbus over the years was 4,001 = 40,001 = 400,001 as they kept increasing the number of registers you could address. At least that's what I think they did. I still get tripped up with Modbus, especially when vendors forget to actually tell you stuff in their manuals.

I really like the Do-more instruction as I don't need to worry how many zeroes to add.

[Controls Guy]

Yeah, I really wish when OEMs give target Modbus addresses, they'd just list the frame address bytes.  Then you can translate it into the convention used by whatever master you're working with.  Sometimes they do the 4xxxx syntax, which is pretty clear, but if they strip the prefix and tell you the address is "1", you don't know if that means Modbus 1 (frame 00 00) or Modbus 2 (frame 00 01).  Then toss in floats and word/byte ordering and it's chaos salad (at least not too hard to unsnarfle, but it does seem unnecessary).

Other than the address, I hate when they describe the protocol byte-by-byte.  You see a twenty page section on Modbus comms and you can't shake the feeling they must be doing something special, but in reality they've just redundantly documented the Modbus protocol in their device docs.  Just give me the addresses and the encoding, please, and if you must, a link to Modbus.org

[DLTimmons]

Talk about confusing Try Prosoft version of Modbus for AB Compact logix. They over lap Coil and register addresses Coil 1 is bit 0 of register 1