Modbus TCP Map - ESP32-8685

Status: Draft| Applies to: SPM/SDM Open WiFi (ESP32-8685) | Firmware: 5.1.11+ | Updated: 2026-06-18

1. Overview

This page documents the Modbus TCP over Wi-Fi interface for the Bituo SPM/SDM series smart meters. It covers connection requirements and the full register map.

---

2. Applied Product Models

This page documents the Modbus TCP over Wi-Fi interface for the Bituo SPM/SDM series smart meters. It covers connection requirements and the full register map.

Single-Phase (SPM01-xxEW)

#	Ordering Number	Description
1	SPM01-D2EW	SPM01 1PN FLEX/63A Wi-Fi (ESP32-8685)
2	SPM01-D1EW	SPM01 1PN MCBM-DM/63A Wi-Fi (ESP32-8685)
3	SPM01-U1EW	SPM01 1PN MCBM-UM/63A Wi-Fi (ESP32-8685)

Split-Phase (SDM02-EW-*)

#	Ordering Number	Description
1	SDM02-EW-12	SDM02 Split-Phase SCTA-2×120A/Φ16 Wi-Fi (ESP32-8685)
2	SDM02-EW-20	SDM02 Split-Phase SCTA-2×200A/Φ20 Wi-Fi (ESP32-8685)
3	SDM02-EW-10U	SDM02 Split-Phase SCTA-2×100A/Φ12 Wi-Fi(ESP32-8685)

Three-Phase (SPM02-xxEW / SDM01-EWM-*)

#	Ordering Number	Description
1	SPM02-D2EW	SPM02 3PN FLEX/63A Wi-Fi (ESP32-8685)
2	SPM02-D1EW	SPM02 3PN MCBM-DM/63A Wi-Fi (ESP32-8685)
3	SPM02-U1EW	SPM02 3PN MCBM-UM/63A Wi-Fi (ESP32-8685)
4	SDM01-EWM-12	SDM01 SCTA-3×120A/Φ16 Wi-Fi (ESP32-8685) + RS485
5	SDM01-EWM-20	SDM01 SCTA-3×200A/Φ20 Wi-Fi (ESP32-8685) + RS485

---

3. Connection & Protocol Notes

💡 Default Connection Parameters: Protocol: Modbus TCP | Port: 502 | Slave ID: 1 | Byte Order: Big-Endian (ABCD)

Critical: Single-Connection Limitation The device firmware supports only ONE concurrent TCP connection** and actively resets the socket after each read request.

Integration Requirement: Open a new TCP connection before each read operation and close it immediately afterward. A minimum delay of 150ms between consecutive reads is recommended to prevent device overload.

Supported Function Codes:

• 0x03 — Read Holding Registers

• 0x04 — Read Input Registers (Both function codes return identical data on this device.)

• 0x06 — Write Single Register (Used for Control Commands only. )

---

4. Register Map

4.1 Product Identification (Base Address: 978)

This section is identical across all Single-Phase, Split-Phase, and Three-Phase devices.

Note: String fields are encoded as continuous UTF-8 byte streams. Register count = Bytes ÷ 2.

Address (DEC)	Address (HEX)	Description	Func Code	R/W	Bytes	Registers	Data Type	Notes
978	0x03D2	MAC Address	03, 04	R	12	6	UTF-8 String	Device Wi-Fi MAC address.
984	0x03D8	Model	03, 04	R	10	5	UTF-8 String	e.g., "SDM01_3PN"
989	0x03DD	MCU Version	03, 04	R	10	5	UTF-8 String	e.g., "5.1.11"
994	0x03E2	RSSI	03, 04	R	2	1	UINT16	Wi-Fi signal strength (dBm). Typical range: -30 ~ -90.
995	0x03E3	System Time	03, 04	R	4	2	UINT32	Unix timestamp (seconds since 1970-01-01).
997	0x03E5	Firmware Version	03, 04	R	6	3	UTF-8 String	Format: "x.x.x"

4.2 Basic Metering Data

All FLOAT32 values occupy 2 Modbus registers (4 bytes). Byte order: Big-Endian (ABCD). Please select the tab corresponding to your device type.

Single-Phase

Address (DEC)	Address (HEX)	Description	Func Code	R/W	Data Type	Range	Unit
1000	0x03E8	Voltage	03, 04	R	FLOAT32	0 – 1000	V
1002	0x03EA	Current	03, 04	R	FLOAT32	0 – 1000	A
1004	0x03EC	Active Power	03, 04	R	FLOAT32	-1000 – 1000	kW
1006	0x03EE	Power Factor	03, 04	R	FLOAT32	-1.0 – 1.0	—
1008	0x03F0	Frequency	03, 04	R	FLOAT32	0 – 1000	Hz
1010	0x03F2	Import Active Energy	03, 04	R	FLOAT32	±1,999,999,999	kWh
1012	0x03F4	Export Active Energy	03, 04	R	FLOAT32	±1,999,999,999	kWh
1014	0x03F6	Total Active Energy (Import + Export)	03, 04	R	FLOAT32	±1,999,999,999	kWh

Split-Phase

Address (DEC)	Address (HEX)	Description	Func Code	R/W	Data Type	Range	Unit
1000	0x03E8	Voltage L1-N	03, 04	R	FLOAT32	0 – 1000	V
1002	0x03EA	Voltage L2-N	03, 04	R	FLOAT32	0 – 1000	V
1006	0x03EE	Current L1	03, 04	R	FLOAT32	0 – 1000	A
1008	0x03F0	Current L2	03, 04	R	FLOAT32	0 – 1000	A
1012	0x03F4	Active Power L1	03, 04	R	FLOAT32	-1000 – 1000	kW
1014	0x03F6	Active Power L2	03, 04	R	FLOAT32	-1000 – 1000	kW
1018	0x03FA	Reactive Power L1	03, 04	R	FLOAT32	-1000 – 1000	kVAR
1020	0x03FC	Reactive Power L2	03, 04	R	FLOAT32	-1000 – 1000	kVAR
1024	0x0400	Apparent Power L1	03, 04	R	FLOAT32	-1000 – 1000	kVA
1026	0x0402	Apparent Power L2	03, 04	R	FLOAT32	-1000 – 1000	kVA
1030	0x0406	Power Factor L1	03, 04	R	FLOAT32	-1.0 – 1.0	—
1032	0x0408	Power Factor L2	03, 04	R	FLOAT32	-1.0 – 1.0	—
1036	0x040C	Average Voltage L-N	03, 04	R	FLOAT32	0 – 1000	V
1038	0x040E	Average Line Current	03, 04	R	FLOAT32	0 – 1000	A
1040	0x0410	Unbalanced Line Currents	03, 04	R	FLOAT32	-300 – 300	%
1042	0x0412	Total Line Currents	03, 04	R	FLOAT32	0 – 3000	A
1044	0x0414	Total Active Power	03, 04	R	FLOAT32	-3000 – 3000	kW
1046	0x0416	Total Reactive Power	03, 04	R	FLOAT32	-3000 – 3000	kVAR
1048	0x0418	Total Apparent Power	03, 04	R	FLOAT32	-3000 – 3000	kVA
1050	0x041A	Total Power Factor	03, 04	R	FLOAT32	-1.0 – 1.0	—
1052	0x041C	Frequency	03, 04	R	FLOAT32	0 – 1000	Hz
1054	0x041E	Total Import Active Energy	03, 04	R	FLOAT32	±1,999,999,999	kWh
1056	0x0420	Total Export Active Energy	03, 04	R	FLOAT32	±1,999,999,999	kWh
1058	0x0422	Total Import & Export Active Energy	03, 04	R	FLOAT32	±1,999,999,999	kWh
1060	0x0424	L1 Import Active Energy	03, 04	R	FLOAT32	±1,999,999,999	kWh
1062	0x0426	L1 Export Active Energy	03, 04	R	FLOAT32	±1,999,999,999	kWh
1064	0x0428	L1 Import & Export Active Energy	03, 04	R	FLOAT32	±1,999,999,999	kWh
1066	0x042A	L2 Import Active Energy	03, 04	R	FLOAT32	±1,999,999,999	kWh
1068	0x042C	L2 Export Active Energy	03, 04	R	FLOAT32	±1,999,999,999	kWh
1070	0x042E	L2 Import & Export Active Energy	03, 04	R	FLOAT32	±1,999,999,999	kWh

Three-Phase

Address (DEC)	Address (HEX)	Description	Func Code	R/W	Data Type	Range	Unit
1000	0x03E8	Voltage A-N	03, 04	R	FLOAT32	0 – 1000	V
1002	0x03EA	Voltage B-N	03, 04	R	FLOAT32	0 – 1000	V
1004	0x03EC	Voltage C-N	03, 04	R	FLOAT32	0 – 1000	V
1006	0x03EE	Current A	03, 04	R	FLOAT32	0 – 1000	A
1008	0x03F0	Current B	03, 04	R	FLOAT32	0 – 1000	A
1010	0x03F2	Current C	03, 04	R	FLOAT32	0 – 1000	A
1012	0x03F4	Active Power A	03, 04	R	FLOAT32	-1000 – 1000	kW
1014	0x03F6	Active Power B	03, 04	R	FLOAT32	-1000 – 1000	kW
1016	0x03F8	Active Power C	03, 04	R	FLOAT32	-1000 – 1000	kW
1018	0x03FA	Reactive Power A	03, 04	R	FLOAT32	-1000 – 1000	kVAR
1020	0x03FC	Reactive Power B	03, 04	R	FLOAT32	-1000 – 1000	kVAR
1022	0x03FE	Reactive Power C	03, 04	R	FLOAT32	-1000 – 1000	kVAR
1024	0x0400	Apparent Power A	03, 04	R	FLOAT32	-1000 – 1000	kVA
1026	0x0402	Apparent Power B	03, 04	R	FLOAT32	-1000 – 1000	kVA
1028	0x0404	Apparent Power C	03, 04	R	FLOAT32	-1000 – 1000	kVA
1030	0x0406	Power Factor A	03, 04	R	FLOAT32	-1.0 – 1.0	—
1032	0x0408	Power Factor B	03, 04	R	FLOAT32	-1.0 – 1.0	—
1034	0x040A	Power Factor C	03, 04	R	FLOAT32	-1.0 – 1.0	—
1036	0x040C	Average Voltage L-N	03, 04	R	FLOAT32	0 – 1000	V
1038	0x040E	Average Line Current	03, 04	R	FLOAT32	0 – 1000	A
1040	0x0410	Unbalanced Line Currents	03, 04	R	FLOAT32	-300 – 300	%
1042	0x0412	Total Line Currents	03, 04	R	FLOAT32	0 – 3000	A
1044	0x0414	Total Active Power	03, 04	R	FLOAT32	-3000 – 3000	kW
1046	0x0416	Total Reactive Power	03, 04	R	FLOAT32	-3000 – 3000	kVAR
1048	0x0418	Total Apparent Power	03, 04	R	FLOAT32	-3000 – 3000	kVA
1050	0x041A	Total Power Factor	03, 04	R	FLOAT32	-1.0 – 1.0	—
1052	0x041C	Frequency	03, 04	R	FLOAT32	0 – 1000	Hz
1054	0x041E	Total Import Active Energy	03, 04	R	FLOAT32	±1,999,999,999	kWh
1056	0x0420	Total Export Active Energy	03, 04	R	FLOAT32	±1,999,999,999	kWh
1058	0x0422	Total Import & Export Active Energy	03, 04	R	FLOAT32	±1,999,999,999	kWh
1060	0x0424	Phase A Import Active Energy	03, 04	R	FLOAT32	±1,999,999,999	kWh
1062	0x0426	Phase A Export Active Energy	03, 04	R	FLOAT32	±1,999,999,999	kWh
1064	0x0428	Phase A Import & Export Active Energy	03, 04	R	FLOAT32	±1,999,999,999	kWh
1066	0x042A	Phase B Import Active Energy	03, 04	R	FLOAT32	±1,999,999,999	kWh
1068	0x042C	Phase B Export Active Energy	03, 04	R	FLOAT32	±1,999,999,999	kWh
1070	0x042E	Phase B Import & Export Active Energy	03, 04	R	FLOAT32	±1,999,999,999	kWh
1072	0x0430	Phase C Import Active Energy	03, 04	R	FLOAT32	±1,999,999,999	kWh
1074	0x0432	Phase C Export Active Energy	03, 04	R	FLOAT32	±1,999,999,999	kWh
1076	0x0434	Phase C Import & Export Active Energy	03, 04	R	FLOAT32	±1,999,999,999	kWh

---

5. Control Commands (Unicast)

Send these commands to a specific device's IP address using Modbus TCP with the target Slave ID.

Write-Only Commands: These registers are write-only and use Function Code `0x06` (Write Single Register). They are not readable. Sending an incorrect write value will have no effect.

Address (DEC)	Address (HEX)	Description	Func Code	R/W	Data Type	Write Value
10000	0x2710	Trigger LED Blinking (Device Locating)	06	W	UINT16	0x5055 (20565)
10001	0x2711	Reset Energy Accumulators	06	W	UINT16	0x51AA (20906)

🔍 Feature: Device Locating via LED When multiple meters are installed in a dense electrical panel, send 0x5055 to a specific device's Slave ID. The target meter's LED will blink rapidly for 15 seconds, allowing field engineers to visually identify the physical device corresponding to that IP/Slave ID.

---