Read Holding Registers (3)
This function code is used to read one or more registers from the drive.
Request
|
Header |
Transaction Identifier |
2 Bytes |
Used for transaction pairing. A Modbus server returns in the response the transaction identifier from the request. |
|
Protocol Identifier |
2 Bytes |
0 = Modbus Protocol |
|
|
Length |
2 Bytes |
6 = Number of following bytes including the unit identifier. |
|
|
Unit Identifier / Slave ID |
1 Byte |
Used by gateway devices. As AKD2G is not a gateway device, this is not used by the drive. It is recommended to send 0xFF for the unit identifier. |
|
|
Data |
Function Code |
1 Byte |
0x03 |
|
Starting Address |
2 Bytes |
0 to 299. See Mapping. |
|
|
Quantity of Registers |
2 Bytes |
1 to 125. How many 16-bit values registers to read. |
Normal Response
|
Header |
Transaction Identifier |
2 Bytes |
Used for transaction pairing. A Modbus server copies in the response the transaction identifier from the request. |
|
Protocol Identifier |
2 Bytes |
0 = Modbus Protocol |
|
|
Length |
2 Bytes |
Number of following bytes including the unit identifier. |
|
|
Unit Identifier / Slave ID |
1 Byte |
Used by gateway devices. As theAKD2G is not a gateway device, the drive returns in the response the unit identifier from the request. |
|
|
Data |
Function Code |
1 Byte |
0x03 |
|
Byte Count |
1 Byte |
How many data bytes follow. This is twice the Quantity of Registers from the request message. 2 × N* |
|
|
Register Value |
2 × N* Bytes |
Data |
*N = Quantity of Registers
Error Response
|
Header |
Transaction Identifier |
2 Bytes |
Used for transaction pairing. A Modbus server copies in the response the transaction identifier from the request. |
|
Protocol Identifier |
2 Bytes |
0 = Modbus Protocol |
|
|
Length |
2 Bytes |
3 = Number of following bytes including the unit identifier. |
|
|
Unit Identifier / Slave ID |
1 Byte |
Used by gateway devices. As AKD2G is not a gateway device, the drive returns in the response the unit identifier from the request. |
|
|
Data |
Function Code |
1 Byte |
0x83 |
|
Exception Code |
1 Byte |
Example
Following is an example of reading the position loop feedback, AXIS1.PL.FB, starting at address 188 (0x00BC), with an actual value of 0x2A05 F200.
Request
|
Header |
Transaction Identifier |
nn nn |
|
Protocol Identifier |
00 00 |
|
|
Length |
00 06 |
|
|
Unit Identifier / Slave ID |
FF |
|
|
Data |
Function |
03 |
|
Starting Address |
00 BC |
|
|
Quantity of Registers |
00 02 |
Response
|
Header |
Transaction Identifier |
nn nn |
|
Protocol Identifier |
00 00 |
|
|
Length |
00 06 |
|
|
Unit Identifier / Slave ID |
FF |
|
|
Data |
Function |
03 |
|
Byte Count |
08 |
|
|
Register 588 |
2A 05 |
|
|
Register 589 |
F2 00 |
