8-6
745 Transformer Management Relay
GE Power Management
8.2 MODBUS PROTOCOL
8 COMMUNICATIONS
8
8.2.9 FUNCTION CODE 03H/04H: READ ACTUAL VALUES/SETPOINTS
Modbus implementation:
Read Holding Registers
GE Power Management implementation:
Read Actual Values or Setpoints
Since some PLC implementations of Modbus only support one of function codes 03h and 04h, the 745 inter-
pretation allows either function code to be used for reading one or more consecutive setpoints or actual values.
The data starting address will determine the type of data being read. Function codes 03h and 04h are therefore
identical.
The GE Power Management implementation of Modbus views "holding registers" as any setpoint or actual
value register in the 745 memory map. Registers are 16 bit (two byte) values transmitted high order byte first.
Thus all GE Power Management setpoints and actual values in the memory map are sent as two byte regis-
ters. This function code allows the master to read one or more consecutive setpoints or actual values from the
addressed slave device.
The maximum number of values that can be read in a single message is 120.
MESSAGE FORMAT AND EXAMPLE:
Request to read 3 register values starting from address 0200 from slave device 11.
Master Query Message:
Example (hex):
SLAVE ADDRESS
11
query message for slave 11
FUNCTION CODE
03
read register values
DATA STARTING ADDRESS: high order byte
02
data starting at address 0200
DATA STARTING ADDRESS: low order byte
00
NUMBER OF REGISTERS: high order byte
00
3 register values = 6 bytes total
NUMBER OF REGISTERS: low order byte
03
CRC: low order byte
06
CRC: high order byte
E3
Field:
Example (hex):
SLAVE ADDRESS
11
response message from slave 11
FUNCTION CODE
03
read register values
BYTE COUNT
06
3 register values = 6 bytes total
DATA #1: high order byte
02
register value in address 0200 = 022B
DATA #1: low order byte
2B
DATA #2: high order byte
00
register value in address 0201 = 0000
DATA #2: low order byte
00
DATA #3: high order byte
00
register value in address 0202 = 0064
DATA #3: low order byte
64
CRC: low order byte
C8
CRC: high order byte
BA
Содержание 745 TRANSFORMER MANAGEMENT RELAY
Страница 30: ...2 8 745 Transformer Management Relay GE Power Management 2 3 SECURITY 2 GETTING STARTED 2 ...
Страница 150: ...5 100 745 Transformer Management Relay GE Power Management 5 10 INVERSE VOLTS PER HERTZ CURVES 5 SETPOINTS 5 ...
Страница 210: ...7 36 745 Transformer Management Relay GE Power Management 7 2 BLOCK DIAGRAMS 7 SCHEME LOGIC 7 ...
Страница 322: ...9 12 745 Transformer Management Relay GE Power Management 9 3 USING 745PC 9 745 PC SOFTWARE 9 ...
Страница 392: ...11 24 745 Transformer Management Relay GE Power Management 11 1 COMMISSIONING SUMMARY 11 SETPOINT TABLES 11 ...
Страница 396: ...A 4 745 Transformer Management Relay GE Power Management A 1 FIGURES AND TABLES APPENDIXA A ...
Страница 398: ...B 2 745 Transformer Management Relay GE Power Management B 1 EU DECLARATION OF CONFORMITY APPENDIXB B ...
Страница 400: ...C 2 745 Transformer Management Relay GE Power Management C 1 WARRANTY INFORMATION APPENDIXC C ...
Страница 406: ...vi 745 Transformer Management Relay GE Power Management ...
Страница 407: ...GE Power Management 745 Transformer Management Relay NOTES ...