adccommunitymod (AutomationDirect) asked a question.
Created Date: August 13,2008
Created By: petersrj
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I am using a DL450 and communicating with a device via Modbus on Port 1. I have several stages which I cycle through and in every stage I check to make sure the port is not busy before trying to write (or read). In my PLC, SP112 (port 1 busy) is constantly on and hence no communication will occur. Even when the CPU is placed in Program Mode, SP112 stays on. I have disconnected the connector, I have made several run-program and program-run transitions but it stays ON. I have a unit in the field that has had the same symptoms. They have always cleared by cycling power to the PLC. I am sure that will work; however, I have the problem in house and would like to find a permanent solution. Any ideas on how/why it occurred? Assuming we can't find out why it occurred is there a way to reset it via ladder?
Created Date: August 15,2008
Created by: stimpsonjcat
You will see this if the RTS/CTS jumper is not present.
So you do need at least the cable connection to the PLC to be there for the port busy bits to toggle.
Created Date: August 15,2008
Created by: Kristjan H
I had a similar situation where my SP113 (Port 1 Error) bit was constantly on. I ended up power cycling the PLC to clear the error. There was nothing connected to port 1 but I was accidentally giving RX commands. It would be great to have a way to soft-reset the bits.
Created Date: August 19,2008
Created by: petersrj
I tried jumping CTS/RTS and that had no affect. I also noticed that I had ~10 VDC on pin 4 and nothing on pin 5. Would I need to tie them to ground or simply tie them together?
Created Date: August 19,2008
Created by: FACTSTech
I tried jumping CTS/RTS and that had no affect. I also noticed that I had ~10 VDC on pin 4 and nothing on pin 5. Would I need to tie them to ground or simply tie them together? Yes tie them together.
Please post your cable wiring from PLC to other device.
PLC Pin---------------------------Other device Pin
2
3
4
5
6
7
Created Date: August 20,2008
Created by: petersrj
Tech Guy,
Right now, I have nothing connected to port 1. I tied 2 to 3 and 4 to 5 to see if that would clear the port busy. I am just surprised that the port can not be cleared with nothing connected to it. Thanks for the help.
Created Date: August 20,2008
Created by: KPrice
petersrj, try re-writing your stages so that you JMP to a stage that has just one comm instruction, use a one-shot to execute the rung with the comm instruction, then use the port not-busy bit to JMP to the next stage. From your description, it sounds like you have the port not-busy bit in the next stage, and are jumping to the next stage before completing the communication (port not busy). Is this correct? What time-out setting do you have? Also it looks like you are trying to "loop-back ". This "loop-back " will not work on the PLC like it does on a PC terminal program. Have you tried the Modbus test programs that run from a PC? These test programs are great for testing. Hope this helps.
Created Date: August 21,2008
Created by: petersrj
I am using stages with a single comm command and I jump between the stages. I used the methodology described at the end of chapter 4 in the manual using an interlock and the port not busy. If this was a programming issue, wouldn't the port busy clear when the unit was put into program mode?
Created Date: August 21,2008
Created by: bcarlton
Just to refresh
If using RS232 ensure pins 4-5 jumpered. If using RS422/RS485 ensure pins 11-19 and 18-23 jumpered (RTS - CTS).\
And by the way, wwe use the method as you described, in each stage wait until not busy then execute the communication command and JMP to the next stage.
Created Date: August 21,2008
Created by: KPrice
petersrj, I can duplicate your problem of locking-up the port and the "port busy " bit staying on by "looping back " (pin 2 to 3 and pin 4 to 5), or by setting the port for 485 2-wire. Does the port busy bit turn off, and the port times-out when no connections are made to the pins, after run/program/run mode changes? (It looks like you 're using RS232.) Is the port set for RS232? Did you talk with Tech Support?
Created Date: September 10,2008
Created by: stimpsonjcat
Just to refresh
If using RS232 ensure pins 4-5 jumpered. If using RS422/RS485 ensure pins 11-19 and 18-23 jumpered (RTS - CTS).\
And by the way, wwe use the method as you described, in each stage wait until not busy then execute the communication command and JMP to the next stage.
Bernie, you are correct of course, these are the jumpers the manual tells you to use.
But in practice I have noticed that the 4-5 jumper will also allow 422/485 traffic. Odd...but there it is.