Case 1: Multi instrument Modbus RTU master station acquisition in water treatment plants (most common)

System architecture: 90-30 CPU 364+IC693PCM311

Port 1 (RS485) is connected to multiple slave stations, including flow meters, pH meters, turbidity meters, residual chlorine analyzers, and multiple frequency converters;

PCM311 runs MegaBasic as a Modbus RTU master station to poll all instruments and collect data on traffic pH、 Frequency data is transmitted to the main CPU register through the PLC backplane shared memory;

Port 2 (RS232) is connected to an on-site serial port printer to print reports and alarm records at regular intervals.

Reason for selection: If Modbus polling is handed over to the PLC main CPU for COMM-REQ, multiple instruments will prolong the scanning cycle, affecting the real-time logic control; PCM independent coprocessor background polling, the main CPU only handles logic and does not interfere with each other.

Scenario: A large number of existing systems in sewage and water treatment plants are being utilized.

Case 2: CCM protocol interconnection between multiple 90-30 PLCs in a factory

System architecture: 3 sets of GE 90-30 PLCs, each equipped with 1 IC693PCM311, Port1 RS422 networking, and GE-CCM protocol.

Exchange between PLCs: equipment operation status, fault signals, production counting, interlocking signals;

PCM is responsible for sending and receiving CCM messages, mapping data to PLC registers, and directly reading and writing registers in ladder diagrams without processing underlying messages.

Business scenario: Segmented control of production line, A section PLC requires interlocking of equipment status in B section; Old projects of steel mills and building materials production lines.

Case 3: Non standard ASCII serial port device gateway conversion (barcode scale, barcode scanner, serial port printer, third-party RTU)

Many old devices have proprietary ASCII serial port protocols, and PLC native serial ports do not support complex parsing. PCM311 uses MegaBasic to write custom protocol parsing:

Port2 RS232 connects to a weighing barcode scale and receives ASCII weight messages from the scale; Extract weight from PCM parsing message and write it into PLC register;

Port1 RS485 interfaces with a third-party serial port RTU to collect temperature and pressure data;

Output the internal alarm information of the PLC to the serial printer through Port2 to print event logs.

Key point: The serial port of the 90-30 CPU itself does not support complex ASCII custom protocols, and PCM311 is used to solve this type of non-standard serial port docking.

Case 4: Centralized polling of multiple frequency converters in metallurgical/cement production lines

Architecture: 90-30+IC693PCM311, Port1 RS485 bus with multiple drive frequency converters.

PCM serves as the Modbus RTU master station, cyclically reading the current, frequency, and fault codes of the frequency converter; Issuing speed settings;

The communication task is completely independent, even if there is interference on the serial bus, it will not slow down the PLC logic scan;

Suitable for old systems with a large number of frequency converters and high communication pressure on the production line.

Case 5: Old SCADA serial port docking (Modbus RTU slave)

PCM311 is configured as a Modbus RTU slave, with RS485 port connected to the old upper SCADA system. The upper system directly reads and writes the PLC’s internal% R and% AI registers;

Difference: The CPU itself can also act as a Modbus slave, but when it has to run other serial port tasks at the same time, it is handed over to PCM to share and release CPU resources.