Data flow example
In this example, the following parameters are read by the controller (PLC address base = 1):
- P1-07 (rated motor voltage, modbus register 107)
- P1-08 (rated motor current, modbus register 108).
Request master → slave (Tx)
Reading register information
Address | Function | Data | CRC check | |||
|---|---|---|---|---|---|---|
Start address | Number of registers | |||||
| Read | High byte | Low byte | High byte | Low byte | crc16 |
01 | 03 | 00 | 6A | 00 | 02 | E4 17 |
Response slave → master (Rx)
Address | Function | Data | CRC check | |||
|---|---|---|---|---|---|---|
Number of data bytes (n) | Information n/2 register | |||||
| Read | High byte | Low byte | Register 107 / 108 | crc16 | |
01 | 03 | 04 | 00 E6 | 00 2B | 5B DB | |
Explanation to the communication example:
Tx = Send from perspective of the bus master.
Address | Device address 0x01 = 1 |
Function | 03 read/06 write |
Start address | Register start address = 0x006A = 106 |
Number of registers | Number of requested registers from start address (register 107/108). |
2 × CRC bytes | CRC_high, CRC_low |
Rx = Received from perspective of the bus master.
Address | Device address 0x01 = 1 |
Function | 03 read/06 write |
Number of data bytes | 0x04 = 4 |
Register 108 high byte | 0x00 = 0 |
Register 108 low byte | 0x2B = 43% of the nominal inverter current |
Register 107 high byte | 0x00 = 0 |
Register 107 low byte | 0xE6 = 230 V |
2 × CRC bytes | CRC_high, CRC_low |
The following example describes the second process data word of the inverter (PLC address base = 1):
Process output data word 2 = modbus register 2 = setpoint speed.
Request master → slave (Tx)
Sending register information
Address | Function | Data | CRC check | |||
|---|---|---|---|---|---|---|
Start address | Information | |||||
| Write | High byte | Low byte | High byte | Low byte | crc16 |
01 | 06 | 00 | 01 | 07 | 00 | DB 3A |
Response slave → master (Rx)
Address | Function | Data | CRC check | |||
|---|---|---|---|---|---|---|
Start address | Information | |||||
| Write | High byte | Low byte | High byte | Low byte | crc16 |
01 | 06 | 00 | 01 | 07 | 00 | DB 3A |
Explanation to the communication example:
Tx = Send from perspective of the bus master.
Address | Device address 0x01 = 1 |
Function | 03 read/06 write |
Start address | Register start address =0x0001 = 1 (first register to be written on = 2 PA2) |
Information | 0700 (setpoint speed) |
2 × CRC bytes | CRC_high, CRC_low |
