In Modbus RTU, what is the standard range of device addresses available for slaves?

• A. 1 to 247
• B. 0 to 255
• C. 1 to 999
• D. 0 to 999

Answer: (A)

In Modbus RTU, the field that selects which device will respond is the unit (or slave) address. For individual slaves, the valid range is one to two hundred forty-seven. Zero is reserved for broadcast, meaning a message sent to address zero is intended for all devices on the network, and devices typically don’t respond to that broadcast the way a single addressed slave would. The addresses two hundred forty-eight to two hundred fifty-five are reserved and not used for standard slaves.

So, up to 247 slaves can be addressed on a single Modbus RTU network, which is why the one-to-two-hundred-forty-seven range is the correct choice.