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CP341 as modbus slave to DCS

Created by: linhmoi at: 5/5/2011 3:36 AM (26 Replies)

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5/5/2011 3:36 AM	Rate (0)
linhmoi Posts: 15 Rating: (0)	[snip] ... My problem is : I ues the example project, connect PLC S7 312, CP341 (RS422/485 type) as modbus slave to DCS communication card (DCS as master) in 2 wire mode. I used example project with modify suitable hardware. On DCS site, the request light is blinking as it sent request command to PLC. But on PLC site, there are not any TXD or RXD blinking (when Power on, they are on for a few second as selt-checking, and then totally off). Could any body tell me the solution? Thank you in advanced. split from: Sample Project of S7300 PLC as Modbus Slave
linhmoi Posts: 15 Rating: (0)	Last edited by: CS Moderator at: 5/6/2011 2:21 PM new subject after splitting Last edited by: linhmoi at: 5/5/2011 8:36 AM
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5/6/2011 2:46 PM	Rate (0)
Kaulquappe Posts: 3093 Rating: (324)	Hello Linhmoi, do you get any error message in the diagnostic buffer of the CP? Regards, Kaulquappe
Kaulquappe Posts: 3093 Rating: (324)
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5/9/2011 11:30 AM	Rate (0)
linhmoi Posts: 15 Rating: (0)	Dear Kaulquappe, Thank for your kind slipt the topic and your reply. There isn't error message in the diagnostic buffer of the CP. The connection bewteen PLC and DCS is via pin 4,11 on CP341 and DCS communication card. On DCS site, it can be sure that all configuration correct. I attach the project as your refference. Pls give me your idea. Thank very much. Attachment Cp341tes.zip (746 Downloads)
linhmoi Posts: 15 Rating: (0)
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5/9/2011 10:04 PM	Rate (0)
Kaulquappe Posts: 3093 Rating: (324)	Hello Linhmoi, as far as I know, the RX LED lights when any character (even one with framing error)is received with the serial interface. The only thing I can think of is a broken cable. Regards, Kaulquappe
Kaulquappe Posts: 3093 Rating: (324)
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5/10/2011 11:02 AM	Rate (0)
linhmoi Posts: 15 Rating: (0)	Dear Kaulquappe, I have allready checked the wiring. The connections as follow: CP341 DCS R(B) pin 11.................Tx+ R(A) pin 4...................Tx- GND..........................GND seting CP341protocol - interface- oprating mode: halfduplex mode, preseting of Recieving line , I tried both none and signal R(A) 0V, R(B)5V. But non of RX, TX led lighting. Could the CP341 have problem? It's a new one. We bought it with new slave dongle and driver. Is there any suggestion?
linhmoi Posts: 15 Rating: (0)
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5/10/2011 12:59 PM	Rate (0)
Kaulquappe Posts: 3093 Rating: (324)	Hello Linhmoi, why do you use TX of the DCS? An X.27 interface has normally got 4 pins for data transmission R+, R-, T+, T-. When you work in 4-wire-mode (RS422) all 4 Pins are used and connected vice versa: R+ to T+,R- to T-. When you work in 2-wire-mode (RS485) the module switch over the transmission line to the receiving line internallywhen they send data. In that case the Pins are connected R+ to R+ and R- to R-. Are your sure, that the DCS works in 2-wire-mode? Regards, Kaulquappe
Kaulquappe Posts: 3093 Rating: (324)
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5/10/2011 4:50 PM	Rate (0)
linhmoi Posts: 15 Rating: (0)	Dear Kaulquappe, I'm sorry for not clear discription. Infact, Tx+ connect to Rx+, Tx- connect to Rx-. Here by attach connection drawing of PLC and DCS. I also tried connect to CP341 DCS R(B) pin 11.................Rx+ R(A) pin 4...................Rx- GND..........................GND but still no of Rx, Tx led light. DCS site:configuration 2 wire, baud rate 9600, Data bit 8, stop bit 1, parity: none Attachment PLC DCS 2wire conenction.zip (688 Downloads)
linhmoi Posts: 15 Rating: (0)
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5/10/2011 5:22 PM	Rate (0)
smiffy Platinum Expert Joined: 1/17/2007 Last visit: 4/15/2025 Posts: 1560 Rating: (540)	You could try swapping over the +/- wires (obviously only at one end). This often works.
	Programming today is the race between software engineers building bigger and better idiot proof programs, and the universe producing bigger and better idiots. So far, the universe is winning...
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5/10/2011 5:35 PM	Rate (0)
Kaulquappe Posts: 3093 Rating: (324)	Hello Linhmoi, when you are sure, that the master addresses slave 2 it should work. I have modified your sample and attached it. I parameterized the ASCII driver, just to see what happens. Use that sample and look in the diagnostic buffer, whether an error message occurs (it should!). Regards, Kaulquappe Attachment Cp341tes1.zip (612 Downloads)
Kaulquappe Posts: 3093 Rating: (324)
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5/10/2011 6:18 PM	Rate (0)
linhmoi Posts: 15 Rating: (0)	smiffy You could try swapping over the +/- wires (obviously only at one end). This often works. Dear Smiffy, I tried it but didn't have a good result. With this connection: CP341 DCS R(B) pin 11.................Rx+ R(A) pin 4...................Rx- GND..........................GND DCS site: only request led blinking PLC site: no Rx, Tx led light. when I swap over CP341 DCS R(B) pin 11.................Rx- R(A) pin 4...................Rx+ GND..........................GND DCS site: both request and recieve led blinking and the same time. PLC site: no Rx, Tx led light. and in both case, DCS have error code : no connection from sub system and no have data. On example project that I attached above, I use only FC3,6,16 to test communication, with Data Block is DB1. @Kaulquappe: I will try to test your modification project when back the company with hardware. Thank you, experts Kaulquappe and Smiffy. I know it losses your time. But this situation make me so confuse!, I read the manual clearly and do it step by step, I tried to test in many cases. But event thought what ever I did, the CP341 Rx, Tx led still no light. That mean no communicate!!!!!. In this case, we have the same project, that PLC S7- 312 is one gateway to tranfer data form ABB DCS (modbus master) to Siemens (CP341 485 Modbus slave) and then to Yokogawa DCS (Modbus master) now working well. Siemens PLC only get data from ABB, tranfer to Yoko DCS with hardware 1 cpu, 2 cp341. I tried to copy this project and deleted 1 cp341, modify program accordingly. But still no working.
linhmoi Posts: 15 Rating: (0)
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