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hamza

Modbus slave

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why guys. I am trying my first project using modbus MCM. the module is my slot is slave. I know where to go to choise length of readdata AND Writedata. but how could I configure the slave to read holding register from(40000....40010) and to write to holding register from(40101....40110). I know to make this configuration with master but I could not make with slave. my master is writing to 40000 ...40010 which I want slave to read it(how I configure the slave) thanks in advance

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Slave means that it waits for the data to come to it. It's passive. If you aren't getting the data in the slave the master isn't sending it correctly. Personally, I'm more used to seeing the range start at 40001 not 40000

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how doea the slave knows that data to be read in place in 40001

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Hello, > how doea the slave knows that data to be read in place in 40001 That is part of the data packet from the master that is defined in the MODBUS protocol. The master can issue a read or a write that includes the type of register 0,1,3,4, the beginning register and the count of registers. Along with protocol required packet wrapper values.

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Can you give your system drawing? so i can see where the master or slave location. and what brand your master and the brand your slave... Edited by raulvirtudazo

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I think you'd have a great place ot start here: http://modbus.org/tech.php

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