Choose a protocol
Usually the other side decides the protocol, so first check what the equipment or system you connect to supports. If you do have a choice, use these guidelines.
At a glance
Section titled “At a glance”| Situation | Product |
|---|---|
| Connect semiconductor or display equipment to a factory host (MES). | SECS/GEM |
| Read and write registers of PLCs, drives, meters, and sensors. | Modbus |
| Integrate equipment from several vendors with SCADA or MES through information models and secure connections. | OPC UA |
| Send measurements through a broker to many subscribers. | OPC UA PubSub with MQTT |
| Test RS-232 or RS-485 communication without serial devices. | Virtual serial ports |
SECS/GEM
Section titled “SECS/GEM”Equipment and hosts exchange messages defined by SEMI standards:
- SECS-II (SEMI E5) defines message structure and data formats. A stream and function number identify each message, such as S1F13.
- HSMS (SEMI E37) carries SECS-II messages over TCP/IP.
- SECS-I (SEMI E4) carries SECS-II messages over an RS-232 serial line, mostly on older equipment.
- GEM (SEMI E30) defines common equipment behavior: establishing communication, control state, variables, reports and events, alarms, remote commands, and recipes.
For GEM300, PDComm provides a declarative capability catalog that records, profile by profile, the GEM300 capabilities of an equipment configuration.
Modbus
Section titled “Modbus”Modbus is a simple request-response protocol in which a client reads and writes four data tables of a server by address: coils, discrete inputs, input registers, and holding registers.
- Modbus TCP runs over Ethernet, on port 502 by default.
- Modbus RTU and ASCII run over RS-485 or RS-232 serial lines. One RS-485 bus connects several devices, told apart by their addresses.
- Modbus/TCP Security protects Modbus TCP with TLS and restricts access by roles in certificates. Its default port is 802.
- A gateway forwards TCP requests to devices on a serial bus.
OPC UA
Section titled “OPC UA”OPC UA (IEC 62541) lets equipment and systems publish data, methods, and events as nodes in an address space.
- Clients browse, read, and write nodes, and receive notifications through subscriptions when values change.
- Certificate-based secure channels sign and encrypt the traffic.
- With PubSub, a publisher sends data sets to many subscribers over UDP or through an MQTT broker.
- The default port is 4840.
MQTT (OASIS MQTT 3.1.1 and 5.0) is a lightweight protocol in which publishers and subscribers exchange messages on topics through a central broker. PDComm provides MQTT as the broker transport of OPC UA PubSub: the OPC UA simulator publishes and subscribes to UADP messages through an MQTT 5.0 broker.
Next steps
Section titled “Next steps”- Check your development environment in Supported platforms and toolchains.
- Run your chosen product right away in the ten-minute first run.