I have a modbus tcp connection between two unit..

Lets say that

PLC_A (Master ) <-> PLC_B (Slave)

Since they are using a modbus tcp connection one can write to a certain coil address and the other one can read that data..

Like A can write on address 0 and B can read from this address..

My question is now where is the complete data table stored, is it stored in the slave or the master?.. More specifically who is the bottleneck in this connection, and limits the size of the memory map of the data table ?

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    \$\begingroup\$ Your question makes no sense. \$\endgroup\$ – Olin Lathrop Jan 5 '17 at 18:16
  • \$\begingroup\$ I am not sure what is not making sense?.. \$\endgroup\$ – Loser Jan 5 '17 at 18:19
  • \$\begingroup\$ The datagram of the package sent to the slave contains a start address, of an data table.. but where is this data table stored? \$\endgroup\$ – Loser Jan 5 '17 at 18:20

A Modbus coil address isn't in any way related to an actual memory address. It's really an identifier of "some output thingy somewhere". It's up to the slave to determine what to do when a specific coil address is specified -- it might store a value in RAM, flip an output bit directly, trigger some other action, or simply ignore it.

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