adccommunitymod (AutomationDirect) asked a question.
Created Date: March 25,2005
Created By: TTP
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I am using a DL-06 PLC to control 2 GS-2 series AC drives. I am connecting the drives to Port 2 via RS-485. The communication works fine if I have only one drive connected at a time, so I don't think it's a problem with the ladder logic. As soon as I connect the second drive, communication fails. I have switched the cables around and either cable seems to work fine by itself. It seems to me like the problem is in the wiring somewhere. DL06: I have setup the DL-06 port 2 according to the manuals (Modbus protocol, basetimeout x1.5, RTS on: 0ms, RTS off: 0ms, station number 1, 9600 baud, 1 stop bit, odd parity). I have followed the port2 pinout in chapter 4 of the dl06 manual for the 485 connection. GS2s: each GS2 drive has a different ID number (one is 2 and the other is 3), they are both set to 485 mode via the 2 dip switches by the comm port.
Created Date: March 25,2005
Created by: TTP
Just thought I'd add some more info incase it helps.
While trying to figure this out... I wrote a ladder program that would use broadcast communication (send to slave address 0) that way either drive would accept the instructions. My program tells the drive to run at 30Hz while I hold down the button on input X0. When the button is not held down, it tells the drive to stop.
So... with both drives connected to the network, I hold the button down. Only one drive turns on and runs. AS SOON as I unplug the running drive, the other one starts running. Likewise, I plug in the first drive again (so they are both connected and running), I release the button to tell the drives to stop. The first drive stops the second one does nothing, I unplug the first drive again, and the second then stops running.
It seems like one drive is "absorbing " all of the communication.
Created Date: March 25,2005
Created by: bcarlton
I'm confused. Is the 'broadcast ' command the normal way you are accomplishing this or just a test?
If you are normally sending a command individually to each drive do both communication sections fail? Or do they complete normally but the drives not respond? If the communications fail have you checked the error code returned?
Does your test program, on the press of the button, send ONE broadcast 'start ' command then wait for the button to be released and send ONE broadcast 'stop ' command?
Created Date: March 25,2005
Created by: TTP
Thanks for the reply, to help clear up:
1) The broadcast mode was just a test to see what was going on
2) The normal operation is to only be operating one drive at a time (Drive 1 runs for a bit then stops, and later drive 2 for a bit and then stops)
3) In both of my programs (the "normal mode " and the broadcast test) I keep sending the commands (either run or stop) to the drives, so not just one command sent, but repeatedly.
4) As far as an error returned, I'm not sure what you mean, is that the value in the "exception response buffer " in the MWX command? If so, the value in that V-memory location never changes from 0. Also, as far as errors go, SP117 never turns on.
Created Date: March 25,2005
Created by: bcarlton
If you are using terminating resistors make sure they are only at the physical endpoints of the line. Is it possible you have them at each drive so that, when both are plugged in, you have three sets of terminations online?
Created Date: March 25,2005
Created by: TTP
Right now I am not using terminating resistors because I read that they are not needed for short cable runs. My cables are only 5 feet long.
Created Date: April 01,2005
Created by: TTP
Aparently one of my drives was bad... no wonder I was having such strange problems!
Created Date: March 25,2005
Created by: TTP
I am using a DL-06 PLC to control 2 GS-2 series AC drives. I am connecting the drives to Port 2 via RS-485. The communication works fine if I have only one drive connected at a time, so I don't think it's a problem with the ladder logic. As soon as I connect the second drive, communication fails. I have switched the cables around and either cable seems to work fine by itself. It seems to me like the problem is in the wiring somewhere.
DL06:
I have setup the DL-06 port 2 according to the manuals (Modbus protocol, basetimeout x1.5, RTS on: 0ms, RTS off: 0ms, station number 1, 9600 baud, 1 stop bit, odd parity). I have followed the port2 pinout in chapter 4 of the dl06 manual for the 485 connection.
GS2s:
each GS2 drive has a different ID number (one is 2 and the other is 3), they are both set to 485 mode via the 2 dip switches by the comm port.