MT4V2 Driver Board Tutorial

STM32F103CB + two DRV8262 chips drive 4 DC motors or DC lights · MODBUS RTU dual serial control · beginner-friendly

1. What is this board?

This is a motor / light driver board. Its core is two DRV8262 dual H-bridge driver chips, controlling 4 DC motors simultaneously, or dimming 4 DC lights (LED / halogen).

From your PC you simply send one command over serial (MODBUS protocol) to run a motor forward, reverse, stop, or set a light to 30%, 80%, and so on.

The board offers two serial ports, either one works:

RS485 port (UART1, differential A/B lines)
UART3 port (PB10/PB11, fixed 115200 baud)

2. Pins & Wiring

2.1 Drive outputs (connect motors / lights)

Purpose	Pins	Channel
Chip1 · Motor 1	IN1 = PB0 , IN2 = PB1	M1
Chip1 · Motor 2	IN3 = PB4 , IN4 = PB5	M2
Chip2 · Motor 3	IN1 = PA0 , IN2 = PA1	M3
Chip2 · Motor 4	IN3 = PA2 , IN4 = PA3	M4

Connect the two drive wires of each motor to INx / INy. The board automatically drives them with a 20 kHz PWM for speed and direction.

2.2 Current sensing

Purpose	Pin	Channel
Motor1 current	chip1_IPROPI1 = PA4	M1
Motor2 current	chip1_IPROPI2 = PA5	M2
Motor3 current	chip2_IPROPI1 = PA6	M3
Motor4 current	chip2_IPROPI2 = PA7	M4

2.3 Control & fault pins

Function	Pin	Description
TOFF	PC13	Off-time / duty clamp config
OCPM	PB2	Overcurrent blanking time select
nSLEEP	PC15	Driver enable (low = sleep)
DECAY	PB8	Decay mode
MODE	PB15	Control mode
nFAULT1	PB12	Chip1 fault (active low, readable)
nFAULT2	PB14	Chip2 fault (active low, readable)

2.4 Serial ports

Purpose	Pins	Parameters
RS485 port (UART1)	TX=PA9, RX=PA10, dir=PA8 (A/B differential)	8N1, baud = factory config (default 38400)
UART3 port	TX=PB10, RX=PB11	fixed 115200, 8N1

3. Communication setup

Slave address: the board uses a fixed MODBUS slave address of 1. No dip switches are needed.

4. MODBUS register map (important)

This is the core table. Learn it and you can control everything.

Register	Function	Access	Value notes
2000	Motor M1 speed	R/W	Signed -100 ~ +100 + = forward, - = reverse, 0 = stop
2001	Motor M2 speed	R/W
2002	Motor M3 speed	R/W
2003	Motor M4 speed	R/W
2010	Motor M1 current (raw ADC)	Read	Motor working current
2011	Motor M2 current	Read
2012	Motor M3 current	Read
2013	Motor M4 current	Read
2020	Chip1 fault nFAULT1	Read	1 = fault, 0 = ok
2021	Chip2 fault nFAULT2	Read	1 = fault, 0 = ok

💡 Master enable (soft coil): the board has no hardware enable signal; use MODBUS soft coil 503 as the "master switch".
1. Default after power-up = ON; the MCU checks it every millisecond.
2. Write 503=ON → motors can run; write 503=OFF → all motors forced to stop.
3. This switch does not block communication; you can turn it back on anytime.

Click to see: hex frames for soft coil 503 (addr = 1)

Enable (motors can run): 01 05 01 F7 FF 00 19 FE
Disable (forced stop):   01 05 01 F7 00 00 58 0E
Read enable status:      01 01 01 F7 00 01 68 0E

Speed is a signed 16-bit value. To write a negative value (e.g. -50) you must send its two's complement (-50 = 0xFFCE). HMI/SCADA tools usually handle this automatically; it only matters when typing hex manually.

5. Hands-on practice (step by step)

Step 0: Prepare tools

A PC + USB-to-serial / USB-to-RS485 adapter
A MODBUS debug tool such as Modbus Poll (free on Windows), or any "serial assistant" that can send raw hex
Connect the adapter to the board's UART3 port (easiest, fixed 115200) or the RS485 port

Step 1: Create a new connection

Create a new connection in Modbus Poll:

Connection > Connect
   Slave ID: 1              (fixed default address)
   Serial port: your COM port
   Baud rate: 115200        (if you use RS485 use 38400 or the factory value)
   Data bits: 8   Parity: None   Stop bits: 1
   Protocol: MODBUS RTU

Step 2: Read registers (confirm it works)

Read 4 registers starting at 2000:

Function (FC): 03  Read Holding Registers
   Starting Address: 2000
   Quantity: 4

If you get back 4 values, communication is OK. Default speed is 0 (motors off).

Step 3: Run motor 1 forward

Write register 2000 with value 50 (50% forward):

FC: 06 Write Single Register
   Register: 2000
   Value: 50

Motor 1 should start running forward at half speed.

Step 4: Reverse, stop, and control the others

What to do	Write register	Value
Motor1 reverse (50%)	2000	-50
Motor1 stop	2000	0
Motor2 forward 100%	2001	100
Motor3 forward 30%	2002	30
Motor4 reverse 80%	2003	-80

Step 5: Brightness control with lights

If you connected DC lights, the speed value becomes "brightness". Write 2000 = 80 for 80% brightness, 0 to switch the light off.

6. Prefer no tools? Send raw hex frames

Use any "serial assistant" in HEX mode and paste one frame below (CRC=Lxx Hxx are the check bytes, already computed). All samples use the fixed address 1.

Motor 1

Action	Full frame (copy & paste)
Forward 50%	01 06 07 D0 00 32 2D 58
Reverse 50%	01 06 07 D0 FF CE 6C E9
Stop	01 06 07 D0 00 00 AC 8D

Motor 2

Action	Full frame
Forward 80%	01 06 07 D1 00 50 FD 71

Multiple writes (FC16 bulk write 2000-2001)

Action	Full frame
M1=50 and M2=50	01 10 07 D0 00 02 04 00 32 00 32 8A C6

Reads

Action	Full frame
Read 4 speeds (2000-2003)	01 03 07 D0 00 04 61 4E
Read 4 currents (2010-2013)	01 03 07 DA 00 04 41 4C
Read 2 faults (2020-2021)	01 03 07 E4 00 02 A0 82

Reading a hex frame at a glance:

01      06      07D0      0032     — 2D58
Addr    Func    Register   Value    CRC check

The address, function, register, and value are plain data; only the trailing CRC is computed. Tools calculate it for you automatically.

7. FAQ

No response / board does nothing?

Check the baud rate: UART3 must be 115200; the RS485 port uses 38400 or the factory value.
Confirm the slave address is 1 (fixed).
Confirm soft coil 503 (master enable) is ON (default ON on power-up).
RS485 wiring: A-to-A, B-to-B, don't swap them; both ends must match baud rate.

Why doesn't writing register 2000 turn the motor on?

The speed register is a "command value" applied to PWM every millisecond. If it doesn't run, check:
1. Enough power (motors need their own supply, not the MCU supply).
2. Soft coil 503 (master enable) is ON (default ON).
3. Read back register 2000 to confirm the write was accepted.

Motor clacks / stalls?

That is usually a PWM duty / configuration issue. Try a smaller speed (e.g. 20%) first, and make sure the motor voltage matches the board supply — avoid over-voltage and over-current.

Reading 2020 / 2021 returns 1?

Fault = 1 means the chip detected overcurrent, overtemperature, or under-voltage. Power off, check the wiring, remove any short, then power back on; once the fault clears, the register returns to 0.

8. Speed value cheat sheet

Desired effect	Register value	Two's complement (HEX)
0 = stop	0	0000
20% forward	20	0014
50% forward	50	0032
100% forward	100	0064
50% reverse	-50	FFCE
100% reverse	-100	FF9C

💡 Three rules to remember: (1) speed lives in registers 2000-2003, one per motor; (2) + = forward, - = reverse, 0 = stop, range ±100; (3) connect at 115200 with a tool like Modbus Poll and you're in control. Enjoy!