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S7-300 /CP341 MODBUS MASTER/SLAVE

Created by: siemens_user_1 at: 12/19/2010 11:56 AM (14 Replies)

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12/19/2010 11:56 AM	Rate (1)
siemens_user_1 Posts: 23 Rating: (1)	Hi everyone I am completely new to Modbus . I use: --S7 300-( CPU-314-1AG-140-AB0) --CP341 (6ES-7341-1CH-020-AE0 ) and trying to make a connection between PLC and MODBUS .PLC is S7-300 that is master ,We have not received the equipments yet .Not the CP 341 card neither the PLC. I already went through the manuals and examples but I dont get where exactly I shouold start from.I have a few questions I will really appreciate if someone answers me : -- What hardware configurations do I need to configure? --What network configuration do I need ? ( I should mention that i cannot see the CP341 interface in NET-PRO . -- What kind of code do I need to use toconnect the CPU to a number of slave devices? -- And finally Is there a way I can test the code before receiving the equipments?(Without PLC AND CP341) I appreciate if someone can help me with any of those questions.
siemens_user_1 Posts: 23 Rating: (1)
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12/19/2010 2:34 PM	Rate (0)
gre_m Posts: 947 Rating: (45)	Hello! Netpro in this casenot needed. You must download from Support (this site) ptp - Point-to-Point Communication software and install it. You can write own programm for CPU314 as modbus master (slave) use ASCII protocol. After install software you can open documentation about CPU and CP, and sample on Step7. You can buy downloadable Modbus driver for CP341.
gre_m Posts: 947 Rating: (45)
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12/20/2010 6:14 AM	Rate (0)
r2407 Posts: 111 Rating: (0)	I have the same problem, specially in writing codes in PLC in order to get data from slaves.
r2407 Posts: 111 Rating: (0)
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12/20/2010 10:34 AM	Rate (0)
siemens_user_1 Posts: 23 Rating: (1)	Thank you Gre_m I bought the CP driver and My main problem is hardware configurations and undrestanding the basic structure of the code .There are 2 types of function blocks I installed , -- P_RCV_RK and P_SND_RK --MOD_341 and MOD_441 (thery are subtrees of Modbus branch ) My undrerstanding is that P_RCV_RK and P_SND_RK transfer the data to the CP341 card but how do we configure CP341 in order to transfer the data to Modbus data lines? I am stucked with this for a while even after buying the CP card and reading the manual I still have problem underestanding the basic concept. I really look forward to hearing your solutions
siemens_user_1 Posts: 23 Rating: (1)
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12/20/2010 10:44 AM	Rate (0)
siemens_user_1 Posts: 23 Rating: (1)	One more thing I found , There are examples in step7 directory with names : "CP_34X_pt" and it contains a few examples such as : "CP340_Ptp connection" "CP341_Protocol 3964" "CP341_Protocol RK-512" "CP341_V24" Which one is more relavant to my case? as you said I should use ASCII protocol but these use different protocols. Shouldnt my protocol be Modbus_master ? Im really confused now ... regards
siemens_user_1 Posts: 23 Rating: (1)
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12/20/2010 11:36 AM	Rate (0)
Kaulquappe Posts: 3093 Rating: (324)	Hello Siemens_user_1, there isan additonalexample for the Modbus communication. Use OPEN -> SAMPLE PROJECTS -> BROWSE and then select zXX21_04_PtP_Com_MODMA or zXX21_04_PtP_Com_MODSL. MODMA is the example when the CP341 is master and MODSL when the CP341 is slave. After you installed the Modbus driver you have to use once BROWSE to see the project in the example list. Regards, Kaulquappe
Kaulquappe Posts: 3093 Rating: (324)	Last edited by: Kaulquappe at: 12/20/2010 11:37 AM
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12/20/2010 1:08 PM	Rate (0)
siemens_user_1 Posts: 23 Rating: (1)	Dear Kualquapper Thank you for your helpful hint, There are still a few things i am getting confused about : --MOD_341 and MOD_441 Function Blocks (these are subtrees of Modbus branch in S7 Library) +Function blocks "IDB_SEND_RK" and "IDB_P_RCV_RK" that the program calls (example program *zXX21_04_PtP_Com_MODMA* ) in FC21 and FC23 These 2 functions have been added toS7 directory after installing Modbus Master/Slave software . Regards Attachment Unknowns.JPG (1725 Downloads)
siemens_user_1 Posts: 23 Rating: (1)
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12/20/2010 2:34 PM	Rate (0)
dchartier Grandmaster-Expert Joined: 9/27/2006 Last visit: 3/19/2025 Posts: 12344 Rating: (2707)	siemens_user_1 +Function blocks "IDB_SEND_RK" and "IDB_P_RCV_RK" that the program calls (example program *zXX21_04_PtP_Com_MODMA* ) in FC21 and FC23 These 2 functions have been added toS7 directory after installing Modbus Master/Slave software . Regards Hello Siemens_user_1; The functions SFB P_SND_RKand SFB P_RCV_RK are the heart of the Modbus master communications, using the CP 341. The datab;locks IDB_xxx_xxx are the instance DBs required to have the SND_ and RCV_ blocks work properly. Please review the sample applivcation program included in the Modbus Master manual, so you can understand how these fuctions and blocks work together to establish Modbus communications with a CP 341 (or a CP 441-2); see the attached document for an illustration. http://support.automation.siemens.com/WW/view/en/1220184 Hope this helps, Daniel Chartier Attachment ModbusMasterBlocks.JPG (1608 Downloads)
	Last edited by: dchartier at: 12/20/2010 3:41 PM
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12/20/2010 3:07 PM	Rate (0)
Kaulquappe Posts: 3093 Rating: (324)	Dear Siemens_user_1, the FB80 and FB180 are only necessary when the CP acts as Modbus slave. Regards, Kaulquappe
Kaulquappe Posts: 3093 Rating: (324)
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This contribution was helpful to 1 thankful Users Ram.Mass

12/21/2010 7:25 AM	Rate (0)
siemens_user_1 Posts: 23 Rating: (1)	Thank You for you reply , I am getting to know how this modbus works gradually There is one more thing im worried about that is about the hardware details I ordered. I attached the project layout for you to see , I am connecting a s7-300 to a number of controllers (so master ) and at the same time the PLC is connected to a DCS in a redundant connection (So slave I guess?? and 2 CP341s required ?? ) What I m worried about is that I ordered 3 CP341 with the same order number of : 6ES7341-1CH02-0AE0 ( is it master or slave ?? ) + 3 Single licenced Modbus master driver + dongle Did I order anything wrong ? Because i think the PLC is slave to the DCS ! can I use master CP341 and master driver to work as slave ? whats the difference between slave and master in case of hardware details ? regards Attachment Project layout.JPG (1208 Downloads)
siemens_user_1 Posts: 23 Rating: (1)
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This contribution was helpful to 1 thankful Users Diego cesa

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