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RS485 Modbus

Created by: Damayanti at: 10/11/2012 3:31 PM (5 Replies)

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10/11/2012 3:31 PM	Rate (0)
Damayanti Bronze Member Joined: 10/17/2011 Last visit: 7/19/2022 Posts: 148 Rating: (3)	Dear Sir, I have IM151-8 PN/DP CPU and with it 6ES7138-4DF11-0AB0 1SI MODBUS/USS Module as a Modbus slave on RS485 Modbus. i want to communicate a SCADA System which is a RS485 MODBUS master with above. Please tell me , how can i send memory address ie flags , timers, counters and DB data to SCADA.? I am using FB81, but i am confused regarding it's configuration in DBs. Please help. Warm regards, Damayanti Bhapkar
	Last edited by: O_Moderator at: 10/12/2012 8:36 AM new subject after splitting from /tf/WW/en/Posts/72742#top
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10/11/2012 4:58 PM	Rate (0)
dchartier Grandmaster-Expert Joined: 9/27/2006 Last visit: 3/23/2025 Posts: 12344 Rating: (2707)	Hello Damayanti; When you are doing Modbus exchanges you have to use Modbus registers and addressing, whichever PLC brand you are using. When using Siemens PLCs., you must create DBs that will be seen as the equivalent to 3000x or 4000x registers from the point of view of the Modbus master. This is described in the modbus slave manual for your Modbus interface. See the attached screencapture. Once you have established the base DB number for each Mocdbus Function you are going to use in the slave, follow the calculationsdescribed in the following sections of the same chapter to finsih the conversion between the S7 and the Modbus addressing. Then you transfer (use Move instructions) the data you want to send to the Modbus master inside these conversion DBs: your timer values, your setpoints, your counters... Then you must make sure the programmer on the master,s side knows where in your DBs you have located the values, and what Modbus registers they correspond to: in other words, you must make a Modbus mapping for your slave. Hope this helps, Daniel Chartier Attachment C:\Users\chard2\Pictures\1SI Modbus conversion table.jpg (299 Downloads)
	Last edited by: dchartier at: 10/11/2012 6:27 PM Last edited by: dchartier at: 10/11/2012 6:23 PM
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10/12/2012 3:23 PM	Rate (0)
Damayanti Bronze Member Joined: 10/17/2011 Last visit: 7/19/2022 Posts: 148 Rating: (3)	Dear Sir, thank you for your reply. I am using one 1SI module as a RS485 Modbus Master and another 1SI module as a modbus slave. I want to read flag from m18.0 to M19.7 ie 16 bits in DB42(SEND source DB) slave_addr=1 function code=1 start addr=w#16#40(64 decimal) no. of bits=16 IN DB80(Conversion DB) DB80.DBW0(aaaaa)=0 DB80.DBW2(bbbbb)=C8 (Decimal=200) DB80.DBW4(uuuuu)=A (Decimal=10) flag byte=[(start addr- aaaaa)/8]+uuuuu =[(64-0)/8]+10 =18 remaining flag bits=[(start adrr-aaaaa)%8] =64%8 =0 therefore flags M18.0 to M19.7 Should be accessed. But when I give request at send, on Tx at Master module and Rx at slave module , blinks. I am getting error_Nr= 16#5e ERROR_INFO= 16#831 Please suggest where it is going wrong? I am attaching the backup copy. Please go through it. Waiting for your reply. Warm regards, Damayanti Bhapkar Attachment 1_support.zip (191 Downloads)

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12/10/2012 9:59 AM	Rate (0)
FrediO Posts: 1 Rating: (0)	Hello Damayanti, Facing the same problem. Did you get this worked out? I get ERROR_NR = W#16#005E and ERROR_INFO = W#16#0811 Tx, Fredi
FrediO Posts: 1 Rating: (0)
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12/10/2012 11:37 AM	Rate (0)
Damayanti Bronze Member Joined: 10/17/2011 Last visit: 7/19/2022 Posts: 148 Rating: (3)	Dear FrediO, please find the program for writing the flags. Damayanti Attachment 1SI_write_flags.zip (209 Downloads)

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This contribution was helpful to 1 thankful Users dchartier

3/11/2015 3:29 PM	Rate (0)
Min_Moderator Platinum Member Joined: 9/3/2014 Last visit: 3/13/2019 Posts: 4766 Rating: (122)	New question published by Damayanti is split to a separate thread with the subject im151-8 pn/dp as a modbus(RS 485 RTU) slave. Best regards Min_Moderator

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