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Is there difference in LTMR registers addressing (by custom logic and communication) between Modbus RTU and modbus TCP?
All TesysT registers accessible by custom logic have the same addresses.
In general, TesysT registers have the same addresses expect the canopen, devicenet or ethernet IP because of different type of addressing (e.g. index/subindex or assembly instead of logic address)
When comparing ModbusTCP with Modbus RTU, there is very little difference.
There are few register with faster refresh data allocated for MOdbusTCP because MOdbusTCP is faster as ModbusRTU. These registers are 2500 – 2507.
Nevertheless, registers 2500-2507 just mirror other registers and so ModbusTCP can use standard registers or mirror registers.

Here is the simple summary of difference:

Read only registers (read by PLC) :
Modbus RTU ---- Modbus TCP
Status 1 register         455                        455 or 2502
Status 2 register         456                        456 or 2503
Logic inputs status     457                        457 or 2504
Logic outputs status   458                        458 or 2505

Read/write registers (written by PLC) :
Modbus RTU ---- Modbus TCP
Control register         704                        704 or 2507

Additionally there might be other few registers related to services available only on Modbus TCP/ethernet,  e.g. SNMP, RSTP, IP address, mask.

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