Modbus 6-digit Addresses
At Quantum Bit Solutions, we have adopted the Modbus 6-digit address scheme for its ease of use and flexibility, moving away from the traditional 4-digit scheme (registers 1-9999).
Why Switch to the 6-Digit Address Scheme?
- Expanded Address Range: The 6-digit scheme supports the full 16-bit address range, from 0 to 65535 registers, as defined in the Modbus Specification. This allows for more comprehensive and scalable addressing.
- Simplified Addressing: The 6-digit address scheme simplifies the addressing process by combining the function code and the full address range into a single long integer value. Instead of two fields, you only need one field to specify the Function Code and Address.
- Consistency: In this scheme, addresses are “1-based,” meaning they start from 1, which aligns with how addresses are decoded by the Modbus Monitor Advanced, Modbus Monitor XPF, and Modbus Monitor App, along with many advanced SCADA and HMIs. This consistency makes it easier to manage and interpret addresses.
Example
The table below shows how the PLC “6-digit” address is decoded by the our Modbus Apps into the function code and the 5-digit Modbus register address:
Modbus Register | Address Scheme | 6-Digit Address | 5-Digit Address | 4-Digit Address1 | Modbus Function Code | Description |
---|---|---|---|---|---|---|
1 | 0x | 000001 | 00001 | 0001 | FC 1 | Read 1st Coil |
1 | 1x | 100001 | 10001 | 0001 | FC 2 | Read 1st Discrete Input |
1 | 3x | 300001 | 30001 | 0001 | FC 4 | Read 1st Input Register |
1 | 4x | 400001 | 40001 | 0001 | FC 3 | Read 1st Holding Register |
65536 | 4x | 465536 | Not Possible2 | Not Possible2 | FC 3 | Read the last possible Holding register |
65536 | 3x | 365536 | Not Possible2 | Not Possible2 | FC 4 | Read the last possible Input register |
Switching to the 6-digit address scheme will streamline your Modbus communication and enhance the overall efficiency of your PLC systems. Make the switch today for a more robust and scalable solution!
More Info:
- Modbus – Wikipedia > Entity numbers and addresses
- YouTube – What is Modbus and how to setup Modbus Monitor Points
- Wikipedia – Modbus
- Modbus for Field Technicians: (Section 3) 5 Digit vs 6 Digit Addressing)
- Brief summary of the section on 5 Digit vs 6 Digit Addressing in “Modbus for Field Technicians”:
- 5 Digit Addressing: Typically used for older PLCs with smaller data memory. It allows addressing up to 65,535 (e.g., 40001 to 49999).
- 6 Digit Addressing: Introduced to accommodate larger data memory in modern PLCs. It allows addressing up to 999,999 (e.g., 400001 to 499999).
- The main difference is the range of addresses that can be referenced, with 6-digit addresses providing a larger range.
- Brief summary of the section on 5 Digit vs 6 Digit Addressing in “Modbus for Field Technicians”: