GE 735

GE Power Management
735/737 Feeder Protection Relay 4-9
4 MODBUS COMMUNICATIONS 4.2 SUPPORTED MODBUS FUNCTIONS
4
Note: for 16 bit transfers hi byte is transmitted first. For example, 0050h is transmitted 00h then 50h
4.2.8 ERROR RESPONSES
When a 735/737 detects an error other than a CRC error, a response will be sent to the master. The most significant bit of
the FUNCTION CODE byte will be set to 1 (that is, the function code sent from the slave will be equal to the function code
sent from the master plus 128). The byte which follows it will be an exception code indicating the type of error that occurred.
Transmissions received from the master with CRC errors will be ignored by the 735/737.
The slave response to an error (other than CRC error) will be:
• SLAVE ADDRESS: 1 byte
• FUNCTION CODE: 1 byte (with MSbit set to 1)
• EXCEPTION CODE: 1 byte
• CRC: 2 bytes
The 735/737 implements the following exception response codes.
• 01: ILLEGAL FUNCTION: The function code transmitted is not one of the functions supported by the 735/737.
• 02: ILLEGAL DATA ADDRESS: The address referenced in the data field transmitted by the master is not an allowable
address for the 735/737.
• 03: ILLEGAL DATA VALUE: The value referenced in the data field transmitted by the master is not within range for the
selected data address.
• 06: BUSY, REJECTED MESSAGE: The transmission was received error-free but the request could not be performed.
• 08: MEMORY PARITY ERROR: A hardware error has occurred in the 735/737. For example, a RAM failure has
occurred and the data requested cannot be sent.
MASTER TRANSMISSION: BYTES EXAMPLE / DESCRIPTION
SLAVE ADDRESS 1 11 message for slave 11
FUNCTION CODE 1 10 store setpoint block
DATA STARTING ADDRESS 2 00 60 first setpoint address 0060h
NUMBER OF SETPOINTS 2 00 0A 10 setpoints
DATA BYTE COUNT 1 14 20 bytes of setpoint data
DATA #1 2 00 06 phase pickup = position 6
DATA #2 2 00 05 phase shape = position 5
DATA #3 2 00 07 phase time multiplier = 7
DATA #4 2 00 01 phase instantaneous = off
DATA #5 2 00 0A ground pickup = 10 (100% of CT)
DATA #6 2 00 08 ground curve shape = 8 (very inverse)
DATA #7 2 00 03 ground time multiplier = 3
DATA #8 2 00 05 ground instantaneous = 5 (0.8 x CT)
DATA #9 2 00 7B phase current = 7B (120%)
DATA #10 2 00 32 ground current = 32 (50%)
CRC 2 ?? ?? CRC calculated by the master
SLAVE RESPONSE: BYTES EXAMPLE / DESCRIPTION
SLAVE ADDRESS 1 11 response message from slave 11
FUNCTION CODE 1 10 store setpoint block
DATA STARTING ADDRESS 2 00 50 block start address
NUMBER OF SETPOINTS 2 00 0A 10 setpoints (2 bytes each)
CRC 2 ?? ?? CRC calculated by the slave