Modbus polling and timeout budget: calculate the slow path
Estimate serial transaction time, include silent intervals and device response, and prevent offline devices from consuming the entire polling cycle.
Modbus
Simple register protocol; RTU on serial, TCP on Ethernet.
The ubiquitous master/slave protocol from 1979: simple register reads and writes over serial (RTU) or Ethernet (TCP, port 502). No discovery, browsing, or security — and present on nearly every PLC, drive, and meter.
Use the concept: Modbus RTU CRC & frame helper · Modbus register decoder & byte-order check · Industrial data connectivity: from register to consumer
In depth
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