How to Fix Eastron SDM630 Modbus Float Decoding Errors
1.12e-40) instead of decimal values.A classic hurdle when integrating EV chargers or EMS dashboards is the Eastron SDM630 Modbus float decoding trap. You establish a stable RS485 connection to the meter and query the Line 1 Voltage (Input Register 30001). Your monitoring software is giving you astronomical scientific notations or completely incomprehensible values, not a normal decimal value like 230.5V.
Polling Register: 30001 (L1 Voltage)
Raw Hex Output: 43 66 80 00
Parsed Int16: 17254
Parsed Float32: 1.12e-40 (Expected: ~230.5 V)
Description: Data type and Endianness mismatch. The master software is interpreting floating-point binary fragments as standard integers.The Eastron SDM series does not transmit simple scaled integers (e.g., sending `2305` and requiring you to multiply by 0.1). Instead, Eastron relies entirely on the IEEE 754 32-bit Single Precision Floating Point standard to transmit exact decimal values over Modbus. If your master device does not know how to stitch these 32 bits back together correctly, the data is entirely unreadable.
Step 1: The Two-Register Requirement
Because the Modbus protocol is fundamentally based on 16-bit registers (Words), a 32-bit Float cannot fit into a single address. Eastron splits the IEEE 754 Float across two consecutive registers.
- To Read Line 1 Voltage (Register 30001) you need to request a length of exactly
2registers (30001 and 30002). - If you only ask for length 1, you are only reading half of the binary footprint of the float. Trying to parse half a float will return garbage.
Step 2: Resolving the Byte Order (Endianness)
Even if you read two registers, the order in which the 4 bytes (A, B, C, D) are arranged might conflict with your software’s native architecture. Eastron generally transmits data in Big-Endian format.
If you read 2 registers and cast them to a Float and the number is still slightly off or completely wacky, then your system has inverted byte ordering. Then go into your SCADA, Node-RED or PLC software, find the Modbus configuration settings and change the Byte Order/Word Swap setting from ABCD to CDAB (or vice-versa) until you see `230.5`.
Still seeing garbage values? Pinpoint exactly which byte order your Eastron meter is transmitting. Paste your raw Hex payload into our free Modbus Endianness Decoder Tool to see all 4 permutations instantly.
The Burden on Traditional PLCs
Configuring a Float32 read with a CDAB byte swap in a modern SCADA or high level scripting language is simply a drop down menu selection. But if you are connecting the Eastron SDM630 to an old industrial PLC with ladder logic, rebuilding IEEE 754 floats is an engineering nightmare.
Every single electrical parameter (Voltage, Current, Power, Energy) needs to be manually bit-shifted and pointer-memory-cast. For large-scale integrations involving dozens of Eastron meters, engineers eliminate this PLC processing burden by deploying an edge protocol gateway.
- Requires complex pointer-casting and bit-shifting algorithms for every single power tag.
- Consumes immense PLC CPU processing time across large meter networks.
- High risk of corrupting the mantissa/exponent logic in older PLCs.
- ASIC hardware natively reconstructs IEEE 754 floats and swaps CDAB instantly.
- Zero mathematical logic required inside the actual PLC program.
- Delivers ready-to-use, clean decimal values to the PLC via Modbus TCP.
Writing complex byte-swap logic in your PLC?
Don’t squander ladder logic memory on Modbus data conversions. Valtoris Edge Gateways natively decode IEEE 754 Floats, swap Endianness and provide perfectly parsed telemetry from Eastron meters straight to your OT or IT networks.
