# SPM/SDM Modbus TCP Map - ESP32-8685 {% hint style="info" %} **Status:** Draft| **Applies to:** SPM/SDM Open WiFi (ESP32-8685) | **Firmware:** 5.1.11+ | **Updated:** 2026-05-25 {% endhint %} ### 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) {% hint style="warning" %} **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. {% endhint %} **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`	RSSI	03, 04	R	2	1	INT16	Wi-Fi signal strength (dBm). Typical range: -30 ~ -90.
979	`0x03D3`	System Time	03, 04	R	4	2	UINT32	Unix timestamp (seconds since 1970-01-01).
981	`0x03D5`	Firmware Version	03, 04	R	6	3	UTF-8 String	Format: "x.x.x"
984	`0x03D8`	MAC Address	03, 04	R	12	6	UTF-8 String	Device Wi-Fi MAC address.
990	`0x03DE`	Model	03, 04	R	10	5	UTF-8 String	e.g., "SDM01_3PN"
995	`0x03E3`	MCU Version	03, 04	R	10	5	UTF-8 String	e.g., "5.1.11"

#### 4.2 Basic Metering Data (Base Address: 1000) *All FLOAT32 values occupy 2 Modbus registers (4 bytes). Byte order: Big-Endian (ABCD). Please select the tab corresponding to your device type.* {% tabs %} {% tab title="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`	Reactive Power	03, 04	R	FLOAT32	-1000 – 1000	kVAR
1008	`0x03F0`	Apparent Power	03, 04	R	FLOAT32	-1000 – 1000	kVA
1010	`0x03F2`	Power Factor	03, 04	R	FLOAT32	-1.0 – 1.0	—
1012	`0x03F4`	Frequency	03, 04	R	FLOAT32	0 – 1000	Hz
1014	`0x03F6`	Import Active Energy	03, 04	R	FLOAT32	±1,999,999,999	kWh
1016	`0x03F8`	Export Active Energy	03, 04	R	FLOAT32	±1,999,999,999	kWh
1018	`0x03FA`	Import & Export Active Energy	03, 04	R	FLOAT32	±1,999,999,999	kWh

{% endtab %} {% tab title="Split-Phase" %}

Address (DEC)	Address (HEX)	Description	Func Code	R/W	Data Type	Range	Unit
Phase A
1000	`0x03E8`	Voltage A-N	03, 04	R	FLOAT32	0 – 1000	V
1002	`0x03EA`	Current A	03, 04	R	FLOAT32	0 – 1000	A
1004	`0x03EC`	Active Power A	03, 04	R	FLOAT32	-1000 – 1000	kW
1006	`0x03EE`	Reactive Power A	03, 04	R	FLOAT32	-1000 – 1000	kVAR
1008	`0x03F0`	Apparent Power A	03, 04	R	FLOAT32	-1000 – 1000	kVA
1010	`0x03F2`	Power Factor A	03, 04	R	FLOAT32	-1.0 – 1.0	—
Phase B
1012	`0x03F4`	Voltage B-N	03, 04	R	FLOAT32	0 – 1000	V
1014	`0x03F6`	Current B	03, 04	R	FLOAT32	0 – 1000	A
1016	`0x03F8`	Active Power B	03, 04	R	FLOAT32	-1000 – 1000	kW
1018	`0x03FA`	Reactive Power B	03, 04	R	FLOAT32	-1000 – 1000	kVAR
1020	`0x03FC`	Apparent Power B	03, 04	R	FLOAT32	-1000 – 1000	kVA
1022	`0x03FE`	Power Factor B	03, 04	R	FLOAT32	-1.0 – 1.0	—
Totals & Energy
1024	`0x0400`	Total Active Power	03, 04	R	FLOAT32	-2000 – 2000	kW
1026	`0x0402`	Total Reactive Power	03, 04	R	FLOAT32	-2000 – 2000	kVAR
1028	`0x0404`	Total Apparent Power	03, 04	R	FLOAT32	-2000 – 2000	kVA
1030	`0x0406`	Total Power Factor	03, 04	R	FLOAT32	-1.0 – 1.0	—
1032	`0x0408`	Frequency	03, 04	R	FLOAT32	0 – 1000	Hz
1034	`0x040A`	Total Import Active Energy	03, 04	R	FLOAT32	±1,999,999,999	kWh
1036	`0x040C`	Total Export Active Energy	03, 04	R	FLOAT32	±1,999,999,999	kWh
1038	`0x040E`	Total Import & Export Active Energy	03, 04	R	FLOAT32	±1,999,999,999	kWh
1040	`0x0410`	Phase A Import Active Energy	03, 04	R	FLOAT32	±1,999,999,999	kWh
1042	`0x0412`	Phase A Export Active Energy	03, 04	R	FLOAT32	±1,999,999,999	kWh
1044	`0x0414`	Phase A Import & Export Active Energy	03, 04	R	FLOAT32	±1,999,999,999	kWh
1046	`0x0416`	Phase B Import Active Energy	03, 04	R	FLOAT32	±1,999,999,999	kWh
1048	`0x0418`	Phase B Export Active Energy	03, 04	R	FLOAT32	±1,999,999,999	kWh
1050	`0x041A`	Phase B Import & Export Active Energy	03, 04	R	FLOAT32	±1,999,999,999	kWh

{% endtab %} {% tab title="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

{% endtab %} {% endtabs %} *** ### 5. Control Commands (Unicast) Send these commands to a specific device's IP address using Modbus TCP with the target **Slave ID**. {% hint style="warning" %} **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. {% endhint %}

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. *** --- # Agent Instructions: Querying This Documentation If you need additional information that is not directly available in this page, you can query the documentation dynamically by asking a question. Perform an HTTP GET request on the current page URL with the `ask` query parameter: ``` GET https://docs.bituo-technik.com/device-api/spm-sdm-modbus-tcp-map-esp32-8685.md?ask= ``` The question should be specific, self-contained, and written in natural language. The response will contain a direct answer to the question and relevant excerpts and sources from the documentation. Use this mechanism when the answer is not explicitly present in the current page, you need clarification or additional context, or you want to retrieve related documentation sections.