Function Codes; Supported Function Codes; 03/04H: Read Actual Values/Settings; Execute Operation - GE UR Series Instruction Manual

B.2 FUNCTION CODES
B.2 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.
FUNCTION CODE
HEX DEC
B
03 3
04 4
05 5
06 6
10 16
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 section MODBUS
ters.
Since some PLC implementations of Modbus
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. The example shows a master device requesting 3
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.
Table B–3: MASTER AND SLAVE DEVICE PACKET TRANSMISSION EXAMPLE
MASTER TRANSMISSION
PACKET FORMAT
SLAVE ADDRESS
FUNCTION CODE
DATA STARTING ADDRESS - hi
DATA STARTING ADDRESS - lo
NUMBER OF REGISTERS - hi
NUMBER OF REGISTERS - lo
CRC - lo
CRC - hi
B-4
MODBUS DEFINITION
Read Holding Registers
Read Holding Registers
Force Single Coil
Preset Single Register
Preset Multiple Registers
®
only support one of function codes 03h and 04h, the relay interpretation
EXAMPLE (HEX)
11
04
40
50
00
03
A7
4A
L90 Line Differential Relay
B.2.1 SUPPORTED FUNCTION CODES
GE POWER MANAGEMENT DEFINITION
Read Actual Values or Settings
Read Actual Values or Settings

Execute Operation

Store Single Setting

Store Multiple Settings

B.2.2 03/04H: READ ACTUAL VALUES/SETTINGS
®
MEMORY MAP for exact details on the data regis-
SLAVE RESPONSE
PACKET FORMAT
SLAVE ADDRESS
FUNCTION CODE
BYTE COUNT
DATA #1 - hi
DATA #1 - lo
DATA #2 - hi
DATA #2 - lo
DATA #3 - hi
DATA #3 - lo
CRC - lo
CRC - hi
APPENDIX B
EXAMPLE (HEX)
11
04
06
00
28
01
2C
00
00
0D
60
GE Power Management