B-4
D30 Line Distance Protection System
GE Multilin
B.2 MODBUS FUNCTION CODES
APPENDIX B
B
B.2MODBUS FUNCTION CODES
B.2.1 SUPPORTED FUNCTION CODES
Modbus officially defines function codes from 1 to 127 though only a small subset is generally needed. The relay supports
some of these functions, as summarized in the following table. Subsequent sections describe each function code in detail.
B.2.2 READ ACTUAL VALUES OR SETTINGS (FUNCTION CODE 03/04H)
This function code allows the master to read one or more consecutive data registers (actual values or settings) from a relay.
Data registers are always 16-bit (two-byte) values transmitted with high order byte first. The maximum number of registers
that can be read in a single packet is 125. See the
Modbus memory map
table for exact details on the data registers.
Since some PLC implementations of Modbus only support one of function codes 03h and 04h. The UR interpretation allows
either function code to be used for reading one or more consecutive data registers. The data starting address will determine
the type of data being read. Function codes 03h and 04h are therefore identical.
The following table shows the format of the master and slave packets in Modbus RTU. Modbus TCP/IP ADUs have a
MBAP instead of slave address, and CRC is in another stack layer. The example shows a master device requesting three
register values starting at address 4050h from slave device 11h (17 decimal); the slave device responds with the values 40,
300, and 0 from registers 4050h, 4051h, and 4052h, respectively.
FUNCTION CODE
MODBUS DEFINITION
GE MULTILIN DEFINITION
HEX
DEC
03
3
Read holding registers
Read actual values or settings
04
4
Read holding registers
Read actual values or settings
05
5
Force single coil
Execute operation
06
6
Preset single register
Store single setting
10
16
Preset multiple registers
Store multiple settings
Table B–4: MASTER AND SLAVE DEVICE PACKET TRANSMISSION EXAMPLE
MASTER TRANSMISSION
SLAVE RESPONSE
PACKET FORMAT
EXAMPLE (HEX)
PACKET FORMAT
EXAMPLE (HEX)
SLAVE ADDRESS
11
SLAVE ADDRESS
11
FUNCTION CODE
04
FUNCTION CODE
04
DATA STARTING ADDRESS - high
40
BYTE COUNT
06
DATA STARTING ADDRESS - low
50
DATA #1 - high
00
NUMBER OF REGISTERS - high
00
DATA #1 - low
28
NUMBER OF REGISTERS - low
03
DATA #2 - high
01
CRC - low
A7
DATA #2 - low
2C
CRC - high
4A
DATA #3 - high
00
DATA #3 - low
00
CRC - low
0D
CRC - high
60
Summary of Contents for D30D00HCHF8AH6AM6BP8BX7A
Page 10: ...x D30 Line Distance Protection System GE Multilin TABLE OF CONTENTS...
Page 374: ...5 248 D30 Line Distance Protection System GE Multilin 5 10 TESTING 5 SETTINGS 5...
Page 398: ...6 24 D30 Line Distance Protection System GE Multilin 6 5 PRODUCT INFORMATION 6 ACTUAL VALUES 6...
Page 410: ...7 12 D30 Line Distance Protection System GE Multilin 7 2 TARGETS 7 COMMANDS AND TARGETS 7...
Page 444: ...9 24 D30 Line Distance Protection System GE Multilin 9 5 FAULT LOCATOR 9 THEORY OF OPERATION 9...
Page 576: ...B 102 D30 Line Distance Protection System GE Multilin B 4 MEMORY MAPPING APPENDIX B B...
Page 616: ...D 10 D30 Line Distance Protection System GE Multilin D 1 IEC 60870 5 104 PROTOCOL APPENDIX D D...
Page 628: ...E 12 D30 Line Distance Protection System GE Multilin E 2 DNP POINT LISTS APPENDIX E E...
Page 636: ...F 8 D30 Line Distance Protection System GE Multilin F 3 WARRANTY APPENDIX F F...
Page 646: ...x D30 Line Distance Protection System GE Multilin INDEX...
