GE 239 MOTOR PROTECTION RELAY

GE 239 MOTOR PROTECTION RELAY

Communication Overview

Protocol standard: Adopting a subset of the Modbus RTU serial communication standard, it is a single master multi slave protocol with 239 relays as slave devices. It does not support master mode and only supports RTU version (binary), not ASCII version.

Application scenario: Monitoring, programming, and control functions can be achieved through read and write register commands, suitable for communication scenarios with multiple device chain connections.

Hardware interface and data transmission

Electrical interface: Use a two-wire RS485 hardware interface for half duplex bidirectional data transmission, requiring a daisy chain configuration with terminal networks installed at both ends (such as Belden 9841 wire with a 120 Ω resistor connected in series with a 1nF ceramic capacitor). Use shielded wires and pay attention to polarity.

Data frame format: Asynchronous transmission, 10 bits per frame (1 start bit+8 data bits+1 stop bit), supports baud rates of 1200, 2400, 4800, 9600, 19200.

Data packet format: Both the master request and the slave response contain the slave address, function code, data, and CRC checksum. The slave address 0 is the broadcast command, and the function code>127 indicates an error response.

Error verification: CRC-16 verification is used. If the verification is incorrect, the slave device will not respond, and the algorithm involves polynomial division. Please refer to the document for specific steps.

Timing requirement: If the received character interval exceeds 3.5 characters, the communication link needs to be reset, such as exceeding 3.65ms at 9600 baud rate.

Supported Modbus Function Codes

03/04: Read set value and actual value, read up to 125 registers (hold register/input register), 16 bit value low byte priority request to read 3 registers starting from 006B at address 11

05: Execute operation, trigger relay action through operation code (such as reset, emergency restart) Reset relay (operation code 1)

06: Store a single set value, write the set value to a single register, and request the device to write 0064 to address 1020

07: Read device status, retrieve device status bytes (alarm, trip, etc. flag bits), request status from address 11

08: Loop back testing, testing communication link integrity, requesting/sending test data 0000 from the device

16: Store multiple set values, batch write up to 60 registers/write 0096 to 1028 and 1029

16 (Execute Command): Execute operations by writing registers. When the PLC does not support the 05 function code, it is necessary to write command function code 5 and operation code to address 0080 and 0081 to perform reset

Memory-mapped

User defined memory area: Address remapping is achieved through register index (0180H-01F7H) and data area (0100H-0177H) to improve data throughput, such as mapping current and temperature values of different addresses to adjacent addresses for reading.

Memory mapping table: Detailed listing of groups, descriptions, ranges, step sizes, units, etc. for each address, including 21 parts such as product information (0000-007F), commands (0080-00FF), user-defined registers (0100-017F), actual values (0200-027F), set values (1000-11EF), covering motor status, fault causes, current, temperature, relay configuration, etc.

Data format: defines the data types and bit masks corresponding to codes F1-F114, such as F1 being an unsigned integer, F5 being a trip reason code, F104 being a product option flag, etc.