Overview
Modbus is a simple communication protocol often used for reporting data from an industrial device to an HMI
Most drive parameters are supported over Modbus TCP (see "Modbus Parameter Table") with the exception of commands which output character strings. For information about the Modbus protocol, see: http://www.Modbus.org/specs.php.
Modbus Installation and Setup
Modbus TCP is provided over the service port on the top of the drive (X11 connector, the connector used for WorkBench). Connect the drive and a device such as an HMI to a working Ethernet network. For ease of testing and configuration, connect a PC running WorkBench to the same network.
After booting, the drive will flash its Ethernet IP address on the front display. The drive can be accessed at this address for Modbus on port 502. WorkBench uses the same address, but a different port number.
Once the devices are connected, the connected device can open a connection to the AKD using these settings:
- IP Address: read from drive display or WorkBench connect screen
- Port: 502
- Add Modbus CRC code: No
Overview of Messaging
All parameters with an internal data width of 32-bit and lower are mapped to Modbus as 32-bit (2 register) values. The contents of both registers must be read or written in the same message, by setting the Starting Address to the lowest index of the parameter and the Quantity of Registers to two.
All parameters with an internal data width of 64-bit are mapped to Modbus as 64-bit (4 register) values. The contents of all four registers must be read or written in the same message by setting the Starting Address to the lowest index of the parameter and the Quantity of Registers to four.
Parameters are scaled as in the Terminal window of WorkBench, but note that floating point values are scaled by an additional factor of 1,000 to retain precision.
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A read attempt of command or write-only parameters will return a value of zero.
Supported Functions
Two Modbus functions are currently supported:
- Read Holding Registers. Function code = 0x03 (3).
- Write Multiple Registers. Function code = 0x10 (16).
To allow only 32-bit and 64-bit access, the quantity of registers is limited to two registers for 32-bit variables and four registers for 64-bit variables. You can also read/write to a single register for certain parameters. Other quantities return an exception response.
Read Holding Registers (0x03)
This function code is used to read all registers of one drive parameter.
Request
|
Function Code |
1 Byte |
0x03 |
|
Starting Address |
2 Bytes |
0x0000-0xFFFF (see "Modbus Parameter Table") |
|
Quantity of Registers |
2 Bytes |
Two 32-bit values or four 64-bit values |
Normal Response
|
Function Code |
1 Byte |
0x03 |
|
Byte Count |
1 Byte |
2 x N* |
|
Register Value |
N* x 2 Bytes |
Data |
*N = Quantity of Registers
Error Response
|
Function Code |
1 Byte |
0x83 |
|
Exception Code |
1 Byte |
Following is an example of reading the position loop feedback PL.FB at index 588 (0x024C), with an actual value of 0x1 2A05 F200.
Request
|
Function |
03 |
|
Starting Address |
02 4C |
|
Quantity of Registers |
00 04 |
Response
|
Function |
03 |
|
Byte Count |
08 |
|
Register 588 |
00 00 |
|
Register 589 |
00 01 |
|
Register 590 |
2A 05 |
|
Register 591 |
F2 00 |
Write Multiple Registers (0x10)
This function code is used to write all registers of one drive parameter.
Request
|
Function Code |
1 Byte |
0x10 |
|
Starting Address |
2 Bytes |
0x0000-0xFFFF (see Modbus index in parameter lists) |
|
Quantity of Registers |
2 Bytes |
2 (32-bit values) or 4 (64-bit values) |
|
Byte Count |
1 Byte |
2 x N* |
|
Register Value |
N* x 2 Bytes |
Data |
*N = Quantity of Registers
Normal Response
|
Function Code |
1 Byte |
0x10 |
|
Starting Address |
2 Bytes |
0x0000-0xFFFF |
|
Quantity of Registers |
2 Bytes |
2 or 4 |
Error Response
|
Function Code |
1 Byte |
0x90 |
|
Exception Code |
1 Byte |
Following is an example of setting the mode of digital input 1 (DIN1.MODE) at index 122 (0x007A) to a value of 3.
Request
|
Function |
10 |
|
Starting Address |
00 7A |
|
Quantity of Registers |
00 02 |
|
Byte Count |
04 |
|
Register 122 |
00 00 |
|
Register 123 |
00 03 |
Response
|
Function |
10 |
|
Starting Address |
00 7A |
|
Quantity of Registers |
00 02 |
Exception Response Codes
Standard Codes
| Description | Exception Code |
|---|---|
|
Illegal Function |
1 |
|
Illegal data address |
2 |
|
Illegal Data Value |
3 |
|
Slave Device Failure |
4 |
|
Acknowledge |
5 |
|
Slave Device Busy |
6 |
|
Memory Parity Error |
8 |
|
Gateway Path Unavailable |
10 |
|
Gateway Target Device Failed To Respond |
11 |
Manufacturer Codes
| Description | Exception Code |
|---|---|
|
Illegal Block Size (must be two registers for 32-bit and four registers for 64-bit parameters) |
32 |
|
Unknown Parameter (bad address) |
33 |
|
Error Processing Command (such as "Data value is greater than maximum") |
34 |
|
Byte Count field is invalid in request |
35 |
Reading Product Serial Numbers Over Modbus
The following register addresses are used to read a serial number over Modbus.
| Description | Modbus Register Address | Attribute |
|---|---|---|
| Amount of registers | 6000 | 16 bit |
| Characters 1 and 2 | 6001 | 16 bit |
| Characters 3 and 4 | 6002 | 16 bit |
| Characters 5 and 6 | 6003 | 16 bit |
| Characters 7 and 8 | 6004 | 16 bit |
| Characters 9 and 10 | 6005 | 16 bit |
| Characters 11 and 12 | 6006 | 16 bit |
For example, the product serial number "R-6789-12345" can be read as follows.
| Modbus Register Address | Value |
|---|---|
| 6000 | 6 |
| 6001 | 0x522D ("R-") |
| 6002 | 0x3637 ("67") |
| 6003 | 0x3839 ("89") |
| 6004 | 0x2D31 ("-1") |
| 6005 | 0x3233 ("23") |
| 6006 | 0x3435 ("45") |
