adccommunitymod (AutomationDirect) asked a question.
DL-05 Modbus
Created Date: October 26,2007
Created By: gmarshall
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I configured port 2 on the DL-05 to use the Modbus protocol at the recommended settings. On the DL-05 I see the RXD LED come on every few seconds but no TXD LED. I setup KepServerEX to send Modbus request at one of my memory locations. The DL05 manual says that "No CPU ladder logic is required to support Modbus slave operation ". What am I doing wrong?
Created Date: October 26,2007
Created by: jackson
You 're not giving us much to go on...
More info please.
- Port settings on both sides
- Cabling
- Memory location you are trying to read
Created Date: October 26,2007
Created by: milldrone
gmarshall,
The DL05 manual says that "No CPU ladder logic is required to support Modbus slave operation "
An "end " statement will be needed to get the plc into run mode. Are you in run mode?
Vaughn
Created Date: October 29,2007
Created by: gmarshall
I have a small application that has been running on the PLC and is still running therefore, the PLC is in run mode. I used the default setting of 9600, etc. of the PLC setting of the secondary comm port of port 2. I did change the timeout to recommended values of 800ms and RTS delay of 5ms. Did not change the setting on the PC because it talked Modbus to another application at 9600 baud. I did have to create a new modbus data to request data at addresses that are on the DL-5 V memory (V1400). The TXD led on the DL-05 does blink every few seconds so I assume requests are being sent, but no RXD LED blinks as a response.
Created Date: October 29,2007
Created by: franji1
Originally posted by gmarshall:
The TXD led on the DL-05 does blink every few seconds so I assume requests are being sent, but no RXD LED blinks as a response.
I think you stated it right in your first post, that the RX is blinking but the TX stays off???
Created Date: October 29,2007
Created by: milldrone
gmarshall,
Your first post says
On the DL-05 I see the RXD LED come on every few seconds but no TXD LED.
The second post says
The TXD led on the DL-05 does blink every few seconds so I assume requests are being sent, but no RXD LED blinks
The problem may be in your cable pinout. Can you detail this please?
edit: I see Franji beat me to the post!
Vaughn
Created Date: October 29,2007
Created by: gmarshall
You are correct I did get the TX and RX mixed up. The PC is transmiting the request and the DL-05 RX2 LED is blinking so I am assuming that the DL-05 is receiving the request. The PLC TX2 LED does not turn on therefore I do not see the PLC sending a response back to the PC which has a Modbus controller running.
Created Date: October 29,2007
Created by: gmarshall
The cable that I am using is the RS232 shielded PC cable purchased from Quantum Automation (D2-DSCBL). Therefore the cable should be correct.
Created Date: October 29,2007
Created by: allukes
What about the staion number? You had this talking to another device you say, does it have the same station number? ALso don't overlook the parity. When you initialize the scratchpad it always sets the parity to ODD which is typically different from most other devices.
Created Date: October 29,2007
Created by: gmarshall
Thanks that was it. The systems defaults to ODD parity while Modbus defaults to EVEN parity. Changing parity fixed the problem. Thanks again. I had not thought about different parity states.
Created Date: October 29,2007
Created by: franji1
Basically, for any serial comm to work, always look at BOTH sides to ensure they are the same:
Baud Rate
Parity
Number of Data Bits
last, but not least, protocol