Modbus
How the protocol actually addresses, encodes and fails — the details that decide whether an integration works on the first afternoon or the third.
What is a Modbus register?
Modbus exposes four separate tables of coils, discrete inputs, input registers and holding registers. What each one is, how wide it is, and why a value can span two of them.
6 min read →Modbus 40001 addressing explained
Why the manual says 40001 and the software asks for 0, where the off-by-one comes from, and how to tell which convention a document is using.
5 min read →Holding registers vs input registers
FC03 and FC04 look almost identical on the wire. What actually differs, why a device may implement both, and how to find out which one holds your value.
4 min read →Modbus float byte order
A 32-bit float spans two registers and vendors disagree about the order. ABCD, BADC, CDAB and DCBA, and how to identify which one a device uses.
6 min read →Modbus exception codes
What each exception response means, what usually causes it, and how to tell an exception apart from a timeout.
5 min read →How to scan Modbus registers
Finding a device's real register map when the documentation is missing or wrong, without hammering the device or writing to it.
6 min read →