The Modbus RTU Communications option supports reads from the following memory types on Modicon controllers:

Coils	0xxxx or 0xxxxx
Inputs	1xxxx or 1xxxxx
Input Registers	3xxxx or 3xxxxx
Holding Registers	4xxxx or 4xxxxx
General Reference	6yxxxx or 6yxxxxx
Holding Registers as Double Precision	D4xxxx or D4xxxxx

The Modbus RTU Communications option supports writes to the following memory types on Modicon controllers:

Coils	0xxxx or 0xxxxx
Holding Registers	4xxxx or 4xxxxx
General Reference	6yxxxx or 6yxxxxx
Holding Registers as Double Precision	D4xxxx or D4xxxxx

Caution: When writing to Coils (0xxxx or 0xxxxx), memory protect and coil disable are overwritten.

On Modicon controllers, coils that are not programmed in the controller logic program are not automatically cleared on power up. This means that if a coil is set to 1, the output will remain HOT until explicitly set to 0.

Writing to Holding Registers overrides the controller memory protect.

More information

Modbus RTU supported memory types.

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