Understanding Serial Number Encoding from Modbus Registers

This guide walks through how to interpret the serial number from the device’s Modbus response and explains the conversion process step by step.

This article applies to the following part numbers:

• R9120
• A8332
• A8911
• A90DC
• A89DC

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What You Receive from the Device​

These devices return their serial number across three 16-bit Modbus registers. These registers contain binary data that must be decoded to reveal the serial number.

Each 16-bit word can be broken down into sets of four bits, which are then individually converted from binary to hexadecimal. When combined, these hex values form the full serial number.

Example Breakdown​

Let’s walk through an example using one of our own serial numbers.

Raw Modbus Register Values (Hex):

• 0x001E
• 0xC6C0
• 0xFFEE

These values correspond to the binary data that, when decoded, reveal the serial number.

• 0 → 0000
• 0 → 0000
• 1 → 0001
• E → 1110
• C → 1100
• 6 → 0110
• C → 1100
• 0 → 0000
• F → 1111
• F → 1111
• E → 1110
• E → 1110

If your Modbus polling software defaults to displaying values as unsigned integers, you might see:

• 0x001E → 30
• 0xC6C0 → 50880
• 0xFFEE → 65518

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Serial Number Patterns​

Since around 2011, serial numbers typically begin with the prefix 001EC6. Older devices may start with 0050C2. Recognizing these patterns can help quickly identify the generation of the device you're working with, and assist with your serial number decoding efforts.