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STEP 7-Micro/WIN - Modbus RTU Master using MBUS_MSG

Created by: scarryblairy at: 2/10/2008 9:12 PM (1 Replies)

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2/10/2008 9:12 PM	Rate (0)
scarryblairy Posts: 2 Rating: (0)	Using Modbus Master Port 1 (v1.2) I want to communicate with a custom Modbus RTU Slave. I would like to know what the actual RS-485byte pattern transmission is when using the Mbus_Msg block. For example, I want to request two bytes of information from the slave. The master request should be - 01,03,00,01,00,01,crc-lsb,crc-msb and the response should be 01,03,02,data-byte,data-byte,crc-lsb,crc-msb. The address of the slave is 01 and the function is 03. Is the following correct? *MBUS_MSB_P1 - (Slave = 1, RW = 0, Addr = 40001, Count = 1, DataPtr = &VB200) Thank you.
scarryblairy Posts: 2 Rating: (0)
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2/15/2008 3:21 PM	Rate (0)
Denilson Pegaia Diamond Member Joined: 9/23/2005 Last visit: 1/9/2026 Posts: 4443 Rating: (1487)	scarryblairy Using Modbus Master Port 1 (v1.2) I want to communicate with a custom Modbus RTU Slave. I would like to know what the actual RS-485byte pattern transmission is when using the Mbus_Msg block. For example, I want to request two bytes of information from the slave. The master request should be - 01,03,00,01,00,01,crc-lsb,crc-msb and the response should be 01,03,02,data-byte,data-byte,crc-lsb,crc-msb. The address of the slave is 01 and the function is 03. Is the following correct? *MBUS_MSB_P1 - (Slave = 1, RW = 0, Addr = 40001, Count = 1, DataPtr = &VB200) Thank you. Hi, I don't have this information, specific to S7-200, but: 1 - You can see a Modbus description on "Loadable Driver for Point-to-Point CPs MODBUS Protocol RTU-Format S7 is Master" http://support.automation.siemens.com/BR/view/en/1220184 2 - You can monitore the telegram with Windows HyperTerminal (as char). 3 - You can look at the Modbus.org for documentation. PS.: Why do you need to know the telegram structure?
	Denilson Pegaia Siemens Industry Sector Technical Support
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