WB-MAI6 Modbus register map

Modes

WB-MAI6 allows these operating modes to be configured for each input:

Voltage measurement — differential or single-ended.
Resistance measurement — differential or single-ended.
Current measurement — single-ended only.

Table 3 fully describes the basic operating modes used for standard sensor measurements.

The Sensor type registers (0xX400, 0xX401) Table 5 for each input accept codes from Table 3 or Table 4. For nonstandard measurements, select the input mode and measurement range manually from Table 3.

Table 3. Device operating modes
Measured signal type	Input mode	HEX code	DEC code	Description	Gain	Measurement range	Accuracy	Output data format	Note
Input disabled	-	0x0000	0	-	-	-	-	-
Measurement of voltage	Single-ended	0x0001	1	Single-ended voltage measurement, figure 1	1...4	2–10 V	±0.5 %	µV
						10–30 V	±1 %
						0–2000 mV	±(0.2% + 50 µV)
	Differential	0x0101	257	Differential voltage measurement from −2 to +2 V relative to iGND, figure 6 Thermocouple voltage measurement, Fig. 7	1...128	±2048 mV	±(0.2% + 30 µV)
Measurement of resistance	Single-ended	0x0002	2	Two-wire resistance measurement, Fig. 3 Connecting dry-contact sensors, Fig. 4	1	0–1 kΩ	(±0.1% + 0.3 Ω)	Ω × 100
						1–100 kΩ	±0.2 %
						100–500 kΩ	±1.5 %
	Differential (three-wire circuit)	0x0102	258	Three-wire resistance measurement, figure 8		0–5000 Ω	±(0.1% + 0.15 Ω)
Measurement of current	Single-ended	0x0003	3	Current measurement from 0 to 20 mA, Fig. 2	1...4	0–20.48 mA	±(0.2% + 1 µA)	nA
Voltage measurement with an external divider WB-VDIV	Single-ended	0x0005	5	Voltage measurement from 0 to 60 V	1...4	0–60 V	±(0.2% + 20 mV)	mV	Since firmware 2.1.0
Voltage measurement with an external divider WB-VDIV	Differential	0x0105	261	Voltage measurement from −30 to +30 V	1...128	±32 V	±(0.2% + 30 µV)	mV	Since firmware 2.4.0
Voltage measurement with a custom external divider	Single-ended	0x0006	6	Measurement range depends on the external divider. Divider output must be within 0–2 V for maximum WB-MAI6 accuracy, or 0–4.5 V for near-maximum accuracy.	1...4		±(0.2% + 50 µV) + external divider error	mV	Since firmware 2.1.0

Supported standard sensor types

Table 4 lists supported standard sensor codes to enter in the Sensor type registers Table 5.

With standard sensors, register values 0xX40A and 0xX40B (gain) are ignored. Standard sensors have code 0x1XXX.

Table 4. Standard sensor types
Sensor code HEX	Sensor code DEC	Description	Raw data format	Converted data format	Accuracy
Thermocouples Operating mode — thermocouple voltage measurement, Fig. 7
0x1000	4096	Type K (chromel–alumel)	µV	°C · 10, °C · 100	±(0.8 °C + 0.2 % · Δt)
		Note: Δt is the difference between the thermocouple temperature and the WB-MAI temperature when the thermocouple connects directly to WB-MAI6 without extension wires.
Two-wire resistance temperature detectors Operating mode — two-wire resistance measurement, Fig. 3
0x1100	4352	Pt 50 (α = 0.00385 °C ^-1)	Ω × 100	°C · 10, °C · 100	±1.5 °C
0x1101	4353	Pt 100 (α = 0.00385 °C ^-1)			±0.8 °C
0x1102	4354	Pt 500 (α = 0.00385 °C ^-1)			±0.2 °C
0x1103	4355	Pt 1000 (α = 0.00385 °C ^-1)			±0.15 °C
0x1110	4368	50P (Russian platinum designation; α = 0.00391 °C ^-1)			±1.5 °C
0x1111	4369	100P (Russian platinum designation; α = 0.00391 °C ^-1)			±0.8 °C
0x1112	4370	500P (Russian platinum designation; α = 0.00391 °C ^-1)			±0.2 °C
0x1113	4371	1000P (Russian platinum designation; α = 0.00391 °C ^-1)			±0.15 °C
0x1120	4384	50M (Russian copper designation; α = 0.00428 °C ^-1)			±1.4 °C
0x1121	4385	100M (Russian copper designation; α = 0.00428 °C ^-1)			±0.7 °C
0x1122	4386	500M (Russian copper designation; α = 0.00428 °C ^-1)			±0.2 °C
0x1123	4387	1000M (Russian copper designation; α = 0.00428 °C ^-1)			±0.14 °C
0x1130	4400	Ni 100 (α = 0.00617 °C ^-1)			±0.5 °C
0x1131	4401	Ni 500 (α = 0.00617 °C ^-1)			±0.13 °C
0x1132	4402	Ni 1000 (α = 0.00617 °C ^-1)			±0.1 °C
0x1701	5889	NTC 10k (B = 3988 K)	Ω × 100	°C · 10, °C · 100	±0.2 °C
0x1702	5890	NTC 10k (B = 3950 K)
0x1703	5891	NTC 100k (B = 3950 K)
0x1704	5892	NTC 10k (B = 3435 K)
0x1705	5893	NTC 10k (B = 3470 K)
0x1706	5894	NTC 5k (B = 3470 K)
0x1707	5895	NTC 1.8k (B = 3380 K)
		Note: excludes wire and contact resistance
Three-wire resistance temperature detectors Operating mode — three-wire resistance measurement, figure 8
0x1200	4608	Pt 50 (α = 0.00385 °C ^-1)	Ω × 100	°C · 10, °C · 100	±0.6 °C
0x1201	4609	Pt 100 (α = 0.00385 °C ^-1)			±0.33 °C
0x1202	4610	Pt 500 (α = 0.00385 °C ^-1)			±0.14 °C
0x1203	4611	Pt 1000 (α = 0.00385 °C ^-1)			±0.13 °C
0x1210	4624	50P (Russian platinum designation; α = 0.00391 °C ^-1)			±0.6 °C
0x1211	4625	100P (Russian platinum designation; α = 0.00391 °C ^-1)			±0.33 °C
0x1212	4626	500P (Russian platinum designation; α = 0.00391 °C ^-1)			±0.14 °C
0x1213	4627	1000P (Russian platinum designation; α = 0.00391 °C ^-1)			±0.13 °C
0x1220	4640	50M (Russian copper designation; α = 0.00428 °C ^-1)			±0.6 °C
0x1221	4641	100M (Russian copper designation; α = 0.00428 °C ^-1)			±0.31 °C
0x1222	4642	500M (Russian copper designation; α = 0.00428 °C ^-1)			±0.13 °C
0x1223	4643	1000M (Russian copper designation; α = 0.00428 °C ^-1)			±0.12 °C
0x1230	4656	Ni 100 (α = 0.00617 °C ^-1)			±0.23 °C
0x1231	4657	Ni 500 (α = 0.00617 °C ^-1)			±0.09 °C
0x1232	4658	Ni 1000 (α = 0.00617 °C ^-1)			±0.08 °C
		Note: Rw is the resistance of each wire. Use identical wires of equal length for terminals P and N.
Current-output sensors Operating mode — current measurement from 0 to 20 mA, Fig. 2
0x1300	4864	0–5 mA	nA	0 mA = lower limit (registers 0xX408 / 0xX409) 5 mA = upper limit (registers 0xX40A / 0xX40B)	±(0.2% + 1 µA)
0x1301	4865	0–20 mA	nA	0 mA = lower limit (registers 0xX408 / 0xX409) 20 mA = upper limit (registers 0xX40A / 0xX40B)	±(0.2% + 1 µA)
0x1302	4866	4–20 mA	nA	4 mA = lower limit (registers 0xX408 / 0xX409) 20 mA = upper limit (registers 0xX40A / 0xX40B)	±(0.2% + 1 µA)
Voltage-output sensors in single-ended mode Operating mode — single-ended voltage measurement, figure 1
0x1400	5120	0–1 V	µV	0 V = lower limit (registers 0xX408 / 0xX409) 1 V = upper limit (registers 0xX40A / 0xX40B)	±(0.2% + 50 µV)
0x1401	5121	0–10 V	µV	0 V = lower limit (registers 0xX408 / 0xX409) 10 V = upper limit (registers 0xX40A / 0xX40B)	±(0.5% + 50 µV)
		Note: WB-MAI inputs in this mode have low impedance (50 µA pull-up) to detect unconnected inputs. Contact the manufacturer to disable this.
Voltage-output sensors in differential mode Operating mode — differential voltage measurement from −2 to +2 V, figure 6
0x1500	5376	−50 to +50 mV	µV	−50 mV = lower limit (registers 0xX408 / 0xX409) 50 mV = upper limit (registers 0xX40A / 0xX40B)	±(0.2% + 30 µV)
Dry-contact sensors Operating mode — two-wire resistance measurement, Fig. 4
0x1600	5632	Dry contact	Ω × 100	0 — sensor open or absent 1 — sensor closed (resistance below 100 Ω)
Hall-effect current sensors Operating mode — single-ended voltage measurement, Fig. 5
0x1800	6144	Output (2.500 ± 0.625) V	A × 10	2.500 V corresponds to 0 A, or the offset (registers 0xX408 / 0xX409) (2.500 + 0.625) V corresponds to the rated value (registers 0xX40A / 0xX40B) Registers 0xX408–0xX40B use A × 10	±(0.2% + 0.3% of current scale) (excluding sensor error)

Register map

In Table 5, the symbol X in a register address is the input number from 1 to 6 (0x1–0x6).

Each input supports differential and single-ended operation. Sensor types for INxP and INxN are therefore set separately in registers 0xX400 and 0xX401, where X is the input number from 1 to 6 in hexadecimal.

Manual gain selection is not recommended. Only gains 1, 2 and 4 are available in single-ended mode.

If INxP is configured for differential operation, INxN configuration registers are ignored. INxN supports only single-ended operation.

Table 5. Modbus registers for measurement-channel configuration and readings
Address HEX	Address DEC	Type	Read/write	Default value	Format	Purpose	Note
Measurement-channel configuration
0xX400	4096·X + 1024	holding	RW	0	Table 3, Table 4, 0 — off	Sensor type for INxP or differential INx (see Tables 3 and 4)
0xX401	4096·X + 1025	holding	RW	0	Table 3, Table 4, 0 — off	Sensor type for INxN (see Tables 3 and 4)
0xX402	4096·X + 1026	holding	RW	20	20, 45, 90, 175, 330, 600, 1000	Data rate for INxP or differential INx, samples/s. For example, 20 gives a sampling time of 1/20 = 0.05 s.
0xX403	4096·X + 1027	holding	RW	20	20, 45, 90, 175, 330, 600, 1000	Data rate for INxN, samples/s.
0xX404	4096·X + 1028	holding	RW	1	1 - 50	Number of consecutive measurements for INxP or differential INx
0xX405	4096·X + 1029	holding	RW	1	1 – 50	Number of consecutive measurements for INxN
0xX406	4096·X + 1030	holding	RW	0	0 - 65000	Low-pass filter time constant for INxP or differential INx, ms
0xX407	4096·X + 1031	holding	RW	0	0 - 65000	Low-pass filter time constant for INxN, ms
0xX408	4096·X + 1032	holding	RW	0	16-bit signed int	Active sensor lower measurement limit for INxP or differential INx
0xX409	4096·X + 1033	holding	RW	0	16-bit signed int	Active sensor lower measurement limit for INxN
0xX40A	4096·X + 1034	holding	RW	10000	16-bit signed int	Active sensor upper measurement limit for INxP or differential INx
0xX40B	4096·X + 1035	holding	RW	10000	16-bit signed int	Active sensor upper measurement limit for INxN
0xX40C	4096·X + 1036	holding	RW	0	0 (automatic), 1, 2, 4, 8, 16, 32, 64, 128	Gain for INxP or differential INx
0xX40D	4096·X + 1037	holding	RW	0	0 (automatic), 1, 2, 4, 8, 16, 32, 64, 128	Gain for INxN
0xX40E	4096·X + 1038	holding	RW	0	1 - 10000	Custom external voltage-divider upper resistor R1 for INxP, kΩ × 10	Since firmware 2.1.0
0xX40F	4096·X + 1039	holding	RW	0	1 - 10000	Custom external voltage-divider upper resistor R1 for INxN, kΩ × 10	Since firmware 2.1.0
0xX410	4096·X + 1040	holding	RW	0	1 - 10000	Custom external voltage-divider lower resistor R2 for INxP, kΩ × 10	Since firmware 2.1.0
0xX411	4096·X + 1041	holding	RW	0	1 - 10000	Custom external voltage-divider lower resistor R2 for INxN, kΩ × 10	Since firmware 2.1.0
Measured values
0xX500	4096·X + 1280	input	R	0	32-bit signed int	Measured value for INxP or differential INx	Error: 0x7FFFFFFF
0xX502	4096·X + 1282	input	R	0	32-bit signed int	Measured value for INxN	Error: 0x7FFFFFFF
0xX504	4096·X + 1284	input	R	0	16-bit signed int	Value converted to physical units for INxP or differential INx	Error: 0x7FFF
0xX505	4096·X + 1285	input	R	0	16-bit signed int	Value converted to physical units for INxN	Error: 0x7FFF
0xX506	4096·X + 1286	input	R	1	16-bit signed int	Current gain for INxP or differential INx
0xX507	4096·X + 1287	input	R	1	16-bit signed int	Current gain for INxN
0x0600	1536	input	R	0	16-bit signed int	Voltage at +5V terminals, mV
0x0601	1537	input	R	0	16-bit signed int	Internal device temperature, °C × 100
0x0700 - 0x070B	1792 - 1803	input	R	0	32-bit signed int × 6	Measured values for IN1P–IN6P	Error: 0x7FFFFFFF; since firmware 2.4.0
0x070C - 0x0717	1804 - 1815	input	R	0	32-bit signed int × 6	Measured values for IN1N–IN6N	Error: 0x7FFFFFFF; since firmware 2.4.0
0x0718 - 0x0723	1816 - 1827	input	R	0	32-bit signed int × 6	Values converted to physical units (temperature: °C × 100) for IN1P–IN6P or differential IN1–IN6	Error: 0x7FFFFFFF; since firmware 2.4.0
0x0724 - 0x072F	1828 - 1839	input	R	0	32-bit signed int × 6	Values converted to physical units for IN1N–IN6N	Error: 0x7FFFFFFF; since firmware 2.4.0
Service registers
0x7400-0x740D, 0x7500-0x7507, 0x8400-0x840D, 0x8500-0x8507	Configuration and data registers for two service calibration channels. See the table above.
0x0629	1577	input	R	0	16-bit signed int	AVCC reference voltage, mV
0x062A	1578	input	R	0	16-bit signed int	Two-wire resistance offset, channels 1–3, P, mΩ
0x062B	1579	input	R	0	16-bit signed int	Two-wire resistance offset, channels 1–3, N, mΩ
0x062C	1580	input	R	0	16-bit signed int	Two-wire resistance offset, channels 4–6, P, mΩ
0x062D	1581	input	R	0	16-bit signed int	Two-wire resistance offset, channels 4–6, N, mΩ
0x062E	1582	input	R	0	16-bit unsigned int	Input scan cycle counter
0x0610	1552	input	R	0	16-bit unsigned int	Input scan cycle duration, ms
0x0800 - 0x80B	2048 - 2059	holding	RW		16-bit signed int	Factory-set calibration coefficients for high-voltage measurement dividers

Common registers

Legend
RO / RW	Read only / Read/Write
Shown in bold	Default register value
xN	Multiply the register value by this factor to obtain the value in the stated units. If omitted, assume 1
⚡	This register supports data transmission using events in Fast Modbus.
FW	Firmware version that introduced the register. Blank means it has always been available.
Error:	Value on error
Grey cell	Service register: purpose, format and contents may change in later firmware

Connection settings, firmware version and other service registers
Address		Register parameters			Description	Values	Note
Dec	Hex	Type	Access	Format	Description	Values	Note
Connection settings
110	0x006E	Holding	RW	u16	RS-485 baud rate. RS-485 connection parameter settings	×100, baud 12 — 1200 bit/s, 24 — 2400 bit/s, 48 — 4800 bit/s, 96 — 9600 bit/s, 192 — 19200 bit/s, 384 — 38400 bit/s, 576 — 57600 bit/s, 1152 — 115200 bit/s
111	0x006F	Holding	RW	u16	RS-485 parity setting	0 — no parity (none), 1 — odd, 2 — even
112	0x0070	Holding	RW	u16	RS-485 stop bits See: stop-bit tolerance	1, 2
128	0x0080	Holding	RW	u16	Device Modbus address (details)
200-219	0x00C8 - 0x00DB	Input	RO	string	Device model
220-244	0x00DC - 0x00F4	Input	RO	string	Firmware build commit hash and branch name (2 characters per register)
250-265	0x00FA - 0x0109	Input	RO	string	Firmware version
266-269	0x010A - 0x010D	Input	RO	u64	Serial number extension
270-271	0x010E - 0x010F	Input	RO	u32	Serial number
290-301	0x0122 - 0x012D	Input	RO	string	Firmware signature
320	0x0140	Input	RO	u16	Firmware version in numeric format (details)	MAJOR
321	0x0141					MINOR
322	0x0142					PATCH
323	0x0143			s16		SUFFIX
324-325	0x0144 - 0x0145	Input	RO	u32	Firmware version in numeric format
326-327	0x0146 - 0x0147	Input	RO	u32	Firmware version in big-endian format
Other information
104-105	0x0068 - 0x0069	Input	RO	u32	Uptime since boot	seconds
120	0x0078	Holding	RW	u16	Reboot device without saving state	Any non-zero value reboots the device
129	0x0081	Holding	RW	u16	Enter firmware update mode for 2 minutes	Any non-zero value enters firmware update mode
330-337	0x014A - 0x0151	Input	RO	string	Bootloader version
130	0x0082	Holding	RW	u16	Disable Status LED	0 — enabled 1 — disabled
131	0x0083	Holding	RW	u16	Enter firmware update mode using the current communication settings. To check whether the firmware and bootloader support this feature, read this register. If reading succeeds and returns `0`, the feature is supported.	Writing 1 enters firmware update mode	Since firmware 2.0.7
113	0x0071	Holding	RW	u16	Delay before replying to a Modbus request	0 - 254 ms
114	0x0072	Holding	RW	u16	Continuous reading across register gaps	0 - disabled 1 - enabled 2 - enabled, retained after reboot
121	0x0079	Input	RO	u16	Current internal 5 V rail voltage	mV
122	0x007A	Input	RO	u16	Minimum internal 5 V rail voltage since boot, without averaging	mV
125	0x007D	Input	RO	u16	Current internal 5 V rail voltage, without averaging	mV
119	0x0077	Input	RO	u16	Minimum microcontroller supply voltage since boot, before averaging	mV
123	0x007B	Input	RO	u16	Microcontroller supply voltage	mV
124	0x007C	Input	RO	s16	Internal microcontroller temperature	x0.1, °C
304-319	0x0130-0x013F	Input	RO	string	Device batch number. Available only on devices manufactured from 21 January 2026.		Since firmware 2.3.0
65402	0xFF7A	Holding	RW	u16	Reset device settings to defaults. Communication settings are retained. The device reboots after the reset.	Writing 1 resets the settings	Since firmware 2.1.4
64256-64383	0xFB00-0xFB7F	Input	RO	u16	FlashFS: free space per page	bytes	Since firmware 2.2.0
64384-64511	0xFB80-0xFBFF	Input	RO	u16	FlashFS: total size of current files per page	bytes
64512-64639	0xFC00-0xFC7F	Input	RO	u16	FlashFS: page fragmentation	0…100 % 0 — all data is current, 100 — no current data
64640-64767	0xFC80-0xFCFF	Input	RO	u16	FlashFS: page erase counter
65504	0xFFE0	Input	RO	u16	Maximum stack usage	bytes 0 — stack corrupted	Since firmware 2.2.0
65505	0xFFE1	Input	RO	u16	Free RAM	bytes
65506	0xFFE2	Input	RO	u16	Used RAM	bytes
65507	0xFFE3	Input	RO	u16	Stack size	bytes
65508	0xFFE4	Input	RO	u16	Cause of last MCU reset	1 — LPWR, 2 — WWDG, 3 — IWDG, 4 — SFT, 5 — POR, 6 — PIN, 7 — OBL, 8 — V18PWR	Since firmware 2.2.0
65509	0xFFE5	Input	RO	u32	Firmware update counter		Since firmware 2.2.0