A controller has to talk to everything from a slow RS-485 sensor to a microsecond-tight EtherCAT servo, and each protocol on that list trades speed for reach. Read a Modbus device first. Then see where each of the others fits.
Modbus is simple: each device is a grid of numbered registers. You ask "read holding register N" and it answers with a 16-bit value. Click a register to read it.
🔌 Serial (RS-232 / RS-485)
Point-to-point, or a slow multidrop bus. It is cheap and rugged, and you will find it on most legacy sensors and meters. Timing is counted in milliseconds, where EtherCAT counts microseconds.
📨 Modbus RTU / TCP
A register-model protocol that runs over serial (RTU) or Ethernet (TCP). It is the common protocol for talking to third-party drives, power meters and gateways.
⚡ EtherCAT
Omron's real-time backbone. One frame services every node per cycle, with timing deterministic to the microsecond. Omron uses it for servos, fast I/O and safety (FSoE).
🔁 Cyclic vs acyclic
Cyclic traffic moves the same I/O every scan (EtherCAT process data). Acyclic traffic sends a request only when the program asks for one, such as a Modbus read or a FINS command, so its timing is set by the job rather than the scan.
You need deterministic, microsecond-tight control of 8 servo axes. Which protocol?