Modbus RTU PWM Output 4CH User Guide

Features

Output uses high-speed opto-isolation; output high-level voltage can be selected via internal jumper
Four independent PWM pulse outputs with adjustable frequency and duty cycle
Supports setting device address (1 ~ 255) for cascading multiple devices via RS485 bus
Onboard voltage regulator chip supports wide 7 V ~ 36 V power supply
Onboard integrated isolated power supply provides stable isolated voltage; the isolated side requires no additional power
Onboard integrated magnetic coupling isolation provides signal isolation, ensuring high reliability and strong anti-interference capability
Onboard resettable fuse and TVS (transient voltage suppression) diode effectively suppress surge voltage and transient spike voltage in the circuit, providing overcurrent, overvoltage, lightning, and electrostatic protection
Built-in watchdog timer ensures stable operation without freezing
Rail-mounted enclosure design, compact size, easy installation
Three external LED indicators for easy monitoring of power status and signal transmission/reception

Product Parameters

Communication Interface	RS485
Communication Baud Rate	4800, 9600, 19200, 38400, 57600, 115200, 128000, 256000
Default Communication Format	9600, N, 8, 1
Modbus Protocol	Standard Modbus RTU protocol
Supply Voltage	DC 7~36 V
Output Voltage	3.3 V or 5 V selectable
Output Current	<30mA, signal type
Pulse Frequency	1 Hz~200 kHz
Pulse Resolution	0.01 Hz
Pulse Accuracy	5‰
Duty Cycle	0~100%
Duty Cycle Resolution	0.01%
Duty Cycle Accuracy	5‰(1 Hz~50 kHz), 1%(50 kHz~200 kHz)

Indicator Light Description

Indicator	Status Description
PWR LED	Power indicator, flashes when MCU is working normally
TXD LED	Transmission indicator, lights up when transmitting data
RXD LED	Reception indicator, lights up when receiving data

Hardware Interface Description

D1~D4 are pulse output terminals, GND is power ground. The PWM output frequency range is 1 Hz~200 kHz.

Hardware Connection Description

Connect the USB TO 485 converter to the target board using jumper wires, connecting A-->A and B-->B as shown in the figure below:

Software Test

SSCOM Serial Debug Assistant

Basic Query Commands

Download the SSCOM Serial Debug Assistant and open it on your computer. Open the corresponding port number, set the baud rate to 9600, select SendHex and Receive, and choose ModbusCRC16 check for the checksum.
Send the following command. Under normal conditions, channel 1 will output a pulse with a frequency of 1 kHz and a duty cycle of 50%.
```
01 10 00 00 00 03 06 00 01 86 A0 13 88
```

Other Commands

If you need to send other commands, select SendHEX, choose ModbusCRC16 check for the checksum, enter the first six bytes of the command, and click SEND, it will automatically add the CRC check code. For example, sending the following command sets channel 1 duty cycle to 20%.
```
01 06 00 02 07 D0
```

For more detailed control commands, please refer to the development protocol.

Modbus Poll Software

The serial software is not convenient for data observation. You can use the Modbus Poll Software to read data. Download and install the Modbus Poll software.
Open the software, select Setup -> Read/Write Definition. Set Slave ID to the actual device address, select Function 16, change Quantity to 12 channels. Click OK to confirm.
Select Connection -> Connect..., choose the corresponding serial port, set baud rate to 9600, 8 data bits, no parity, 1 stop bit. Click OK to connect.
After successful connection, set the frequency format. Select registers 0, 3, 6, 9 and set their format to Unsigned 32-bit Big-endian. You can also add register notes in the Alias column.
Enter the channel frequency and duty cycle in the registers; the corresponding pulse will be output. Frequency range: 100~~100000000, i.e., 1 Hz~~200 kHz. Duty cycle range: 0~~10000, i.e., 0~~100%. The figure below shows the settings: Channel 1: 500 Hz, 10%; Channel 2: 1 kHz, 30%; Channel 3: 5 kHz, 50%; Channel 4: 10 kHz, 90%.

Secondary Development Protocol

Function Code Introduction

Function Code	Description
03	Read Holding Registers
06	Write Single Holding Register
10	Write Multiple Holding Registers

Register Address Description

Address (HEX)	Address Storage Content	Register Value	Access	Modbus Function Code
4x0000 4x0001	Channel 1 Frequency High 16-bit Channel 1 Frequency Low 16-bit	Value is unsigned 32-bit hexadecimal, unit 0.01 Hz, range: 100~20000000, i.e., 1 Hz~200 kHz	Read/Write	0x03,0x06,0x10
4x0002	Channel 1 Duty Cycle	Value is unsigned 16-bit hexadecimal, unit 0.01%, range 0~1000, i.e., 0~100%	Read/Write	0x03,0x06,0x10
4x0003 4x0004	Channel 2 Frequency High 16-bit Channel 2 Frequency Low 16-bit	Value is unsigned 32-bit hexadecimal, unit 0.01 Hz, range: 100~20000000, i.e., 1 Hz~200 kHz	Read/Write	0x03,0x06,0x10
4x0005	Channel 2 Duty Cycle	Value is unsigned 16-bit hexadecimal, unit 0.01%, range 0~1000, i.e., 0~100%	Read/Write	0x03,0x06,0x10
4x0006 4x0007	Channel 3 Frequency High 16-bit Channel 3 Frequency Low 16-bit	Value is unsigned 32-bit hexadecimal, unit 0.01 Hz, range: 100~20000000, i.e., 1 Hz~200 kHz	Read/Write	0x03,0x06,0x10
4x0008	Channel 3 Duty Cycle	Value is unsigned 16-bit hexadecimal, unit 0.01%, range 0~1000, i.e., 0~100%	Read/Write	0x03,0x06,0x10
4x0009 4x000A	Channel 4 Frequency High 16-bit Channel 4 Frequency Low 16-bit	Value is unsigned 32-bit hexadecimal, unit 0.01 Hz, range: 100~20000000, i.e., 1 Hz~200 kHz	Read/Write	0x03,0x06,0x10
4x000B	Channel 4 Duty Cycle	Value is unsigned 16-bit hexadecimal, unit 0.01%, range 0~1000, i.e., 0~100%	Read/Write	0x03,0x06,0x10
4x2000	Serial Port Parameters	High byte: parity mode: 0x00~0x02 Low byte: baud rate mode: 0x00~0x07	Read/Write	0x03,0x06
4x4000	Device Address	Stores Modbus address directly Device address: 0x0001-0x00FF	Read/Write	0x03,0x06
4x8000	Software Version	Convert to decimal, then shift decimal point two places left for version 0x0064 = 100 = V1.00	Read	0x03

Note: It is recommended to use function code 10 to set frequency with multiple registers simultaneously. Using function code 06 to operate a single register may output an unknown frequency.

Operation Command Description

Set Channel Output Command

Transmission Code: 01 10 00 00 00 03 06 00 01 86 A0 13 88 FF 7C

Field	Description	Note
01	Device Address	0x00 indicates broadcast address; 0x01-0xFF indicate device address
10	Write Multiple Registers Command
00 00	Register Start Address	Channel start register
00 03	Number of Registers	Number of registers to set
06	Byte Count	Number of output bytes
00 01 86 A0 13 88	Register Data Frequency High 16-bit Frequency Low 16-bit Duty Cycle	Frequency is unsigned 32-bit hexadecimal, unit 0.01 Hz, range: 100~20000000, i.e., 1 Hz~200 kHz Duty Cycle is unsigned 16-bit hexadecimal, unit 0.01%, range 0~1000, i.e., 0~100%
FF 7C	CRC16	CRC16 checksum of the first 6 bytes of data

Return Code: 01 10 00 00 00 03 80 08

Field	Description	Notes
01	Device Address	0x00 indicates broadcast address; 0x01-0xFF indicate device address
10	Write Multiple Registers Command
00 00	Register Start Address	0x0000 - 0x0007 correspond to output channels 1~8
00 03	Number of Registers	Number of registers set, cannot exceed maximum channel count
80 08	CRC16	CRC16 checksum of the first 6 bytes of data

Example: Device address 1

Set channel 2 output 200 Hz 10% duty cycle : 01 10 00 00 00 03 06 00 00 4E 20 03 E8 F0 DC
Set channels 1\~4 output 1 kHz 50% duty cycle : 01 10 00 00 00 0C 18 00 01 86 A0 13 88 00 01 86 A0 13 88 00 01 86 A0 13 88 00 01 86 A0 13 88 6E E5

Set Channel Frequency Command

Transmission Code: 01 10 00 00 00 02 04 00 01 86 A0 C0 77

Field	Description	Notes
01	Device Address	0x00 indicates broadcast address; 0x01-0xFF indicate device address
10	Write Multiple Registers Command
00 00	Register Start Address	Channel start register, 00 00 indicates channel 1 start register
00 02	Number of Registers	Number of registers to set, value is unsigned 32-bit hexadecimal, each register is 16-bit
04	Byte Count	Number of output bytes
00 01 86 A0	Register Data Frequency High 16-bit Frequency Low 16-bit	Frequency is unsigned 32-bit hexadecimal, unit 0.01 Hz, range: 100~20000000, i.e., 1 Hz~200 kHz
C0 77	CRC16	CRC16 checksum of the first 6 bytes of data

Return Code: 01 10 00 00 00 02 41 C8

Field	Description	Notes
01	Device Address	0x00 indicates broadcast address; 0x01-0xFF indicate device address
10	Write Multiple Registers Command
00 00	Register Start Address	0x0000 - 0x0007 correspond to output channels 1~8
00 02	Number of Registers	Number of registers set, cannot exceed maximum channel count
41 C8	CRC16	CRC16 checksum of the first 6 bytes of data

Example: Device with address 1

Set channel 2 output 200 Hz : 01 10 00 00 00 02 04 00 00 4E 20 C7 D7

Set Channel Duty Cycle Command

Transmission Code: 01 06 00 02 07 D0 2B A6

Field	Description	Notes
01	Device Address	0x00 indicates broadcast address; 0x01-0xFF indicate device address
06	06 Command	Write Single Holding Register
00 02	Register Address	Channel 1 duty cycle register
07 D0	Register Data	Duty cycle is unsigned 16-bit hexadecimal, unit 0.01%, range 0~1000, i.e., 0~100%
2B A6	CRC16	CRC16 checksum of the first 6 bytes of data

Return Code: 01 06 00 02 07 D0 2B A6

Field	Description	Notes
01	Device Address	0x00 indicates broadcast address; 0x01-0xFF indicate device address
06	06 Command	Write Single Holding Register
00 02	Register address	Channel duty cycle register
07 D0	Register Data	Duty cycle is unsigned 16-bit hexadecimal, unit 0.01%, range 0~1000, i.e., 0~100%
2B A6	CRC16	CRC16 checksum of the first 6 bytes of data

Example: Device with address 1

Set channel 1 duty cycle 20% : 01 06 00 02 07 D0 2B A6
Set channel 2 duty cycle 50% : 01 06 00 05 13 88 94 9D
Set channel 4 duty cycle 20% : 01 06 00 0B 23 28 E1 26

Read Channel Output Command

Transmission Code: 01 03 00 00 00 0C 45 CF

Field	Description	Notes
01	Device Address	0x00 indicates broadcast address; 0x01-0xFF indicate device address
03	03 Command	Read Holding Registers
00 00	Register Start Address	0x0000 - 0x0007 correspond to input channels 1~8
00 0C	Number of Registers	Number of registers to read, cannot exceed maximum channel count
45 CF	CRC16	CRC16 checksum of the first 6 bytes of data

Return Code: 01 03 18 00 01 86 A0 13 88 00 01 86 A0 13 88 00 01 86 A0 13 88 00 01 86 A0 13 88 90 CE

Field	Description	Notes
01	Device Address	0x00 indicates broadcast address; 0x01-0xFF indicate device address
03	03 Command	Read Holding Registers
18	Byte Count	Total bytes of returned status information
00 01 86 A0 13 88 ……	Output Values	Sequentially frequency and duty cycle for channels 1~4 Frequency is unsigned 32-bit hexadecimal, unit 0.01 Hz, range: 100~20000000, i.e., 1 Hz~200 kHz Duty Cycle is unsigned 16-bit hexadecimal, unit 0.01%, range 0~1000, i.e., 0~100%
90 CE	CRC16	CRC16 checksum of the first 6 bytes of data

Example: Device with address 1

Read channel 1 data : 01 03 00 00 00 03 05 CB
Read channel 1 duty cycle : 01 03 00 02 00 01 25 CA
Read channel 3 data : 01 03 00 06 00 03 E5 CA

Set Baud Rate Command

Transmission Code: 00 06 20 00 00 05 43 D8

Field	Description	Notes
00	Device Address	0x00 indicates broadcast address; 0x01-0xFF indicate device address
06	06 Command	Set baud rate, set device address
20 00	Command Register	0x2000 for setting baud rate, 0x4000 for setting device address
00	Parity Mode	0x00 for no parity, 0x01 for odd parity, 0x02 for even parity
05	Baud Rate Value	Baud rate value mapping: 0x00: 4800 0x01: 9600 0x02: 19200 0x03: 38400 0x04: 57600 0x05: 115200 0x06: 128000 0x07: 256000
43 D8	CRC16	CRC16 checksum of the first 6 bytes of data

Return Code: 00 06 20 00 00 05 43 D8

Field	Description	Notes
00	Device Address	0x00 indicates broadcast address; 0x01-0xFF indicate device address
06	06 Command	Set baud rate, set device address
20 00	Command Register	0x2000 for setting baud rate, 0x4000 for setting device address
00	Parity Mode	0x00 for no parity, 0x01 for odd parity, 0x02 for even parity
05	Baud Rate	Baud rate value mapping: 0x00: 4800 0x01: 9600 0x02: 19200 0x03: 38400 0x04: 57600 0x05: 115200 0x06: 128000 0x07: 256000
43 D8	CRC16	CRC16 checksum of the first 6 bytes of data

Example: Device with address 1

Set baud rate 4800 : 00 06 20 00 00 00 83 DB
Set baud rate 9600 : 00 06 20 00 00 01 42 1B
Set baud rate 115200 : 00 06 20 00 00 05 43 D8

Set Device Address Command

Transmission Code: 00 06 40 00 00 01 5C 1B

Field	Description	Notes
00	Device Address	0x00 indicates broadcast address; 0x01-0xFF indicate device address
06	06 Command	Set baud rate, set device address
40 00	Command Register	0x2000 for setting baud rate, 0x4000 for setting device address
00 01	Device Address	Device address set, 0x0001-0x00FF
5C 1B	CRC16	CRC16 checksum of the first 6 bytes of data

Return Code: 00 06 40 00 00 01 5C 1B

Field	Description	Notes
00	Device Address	0x00 indicates broadcast address; 0x01-0xFF indicate device address
06	06 Command	Set baud rate, set device address
40 00	Command Register	0x2000 for setting baud rate, 0x4000 for setting device address
00 01	Device Address	Device address set, 0x0001-0x00FF
5C 1B	CRC16	CRC16 checksum of the first 6 bytes of data

Example: Device with address 1

Set device address to 0x01 : 00 06 40 00 00 01 5C 1B
Set device address to 0x02 : 00 06 40 00 00 02 1C 1A
Set device address to 0x03 : 00 06 40 00 00 03 DD DA

Read Device Address Command

Transmission code: 00 03 40 00 00 01 90 1B

Field	Description	Notes
00	Device Address	0x00 indicates broadcast address; 0x01-0xFF indicate device address
03	03 Command	Read device address command
40 00	Command Register	0x4000 for reading device address, 0x8000 for reading software version
00 01	Byte Count	Fixed 0x0001
90 1B	CRC16	CRC16 checksum of the first 6 bytes of data

Return code: 01 03 02 00 01 79 84

Field	Description	Notes
01	Device Address	0x00 indicates broadcast address; 0x01-0xFF indicate device address
03	03 Command	Read software version, read device address command
02	Byte Count	Returned byte count
00 01	Device Address	Device address set, 0x0001-0x00FF
79 84	CRC16	CRC16 checksum of the first 6 bytes of data

Example: Device with address 2

Transmission Code: 00 03 40 00 00 01 90 1B
Return Code : 02 03 02 00 02 7D 85 //Address 0x02

Read Software Version Command

Transmission Code: 00 03 80 00 00 01 AC 1B

Field	Description	Notes
00	Device Address	0x00 indicates broadcast address; 0x01-0xFF indicate device address
03	03 Command	Read software version, read device address command
80 00	Command Register	0x4000 for reading device address, 0x8000 for reading software version
00 01	Byte Count	Fixed 0x0001
AC 1B	CRC16	CRC16 checksum of the first 6 bytes of data

Return Code: 01 03 02 00 64 B9 AF

Field	Description	Notes
01	Device Address	0x00 indicates broadcast address; 0x01-0xFF indicate device address
03	03 Command	Read software version, read device address command
02	Byte Count	Returned byte count
00 64	Software Version	Convert to decimal, then shift decimal point two places left for version 0x0064 = 100 = V1.00
B9 AF	CRC16	CRC16 checksum of the first 6 bytes of data

Example: Device with address 1

Transmission Code: 00 03 80 00 00 01 AC 1B
Return Code: 01 03 02 00 64 B9 AF //0x0064 = 100 =V1.00

Exception Function Code Introduction

If the received command is incorrect or an exception occurs, the device will return an exception response. The exception response format is as follows:

Return Code: 01 85 03 02 91

Field	Description	Notes
01	Device Address	0x00 indicates broadcast address; 0x01-0xFF indicate device address
85	Exception Function Code	Exception function code = Request function code + 0x80
03	Byte Count	Exception code
02 91	CRC16	CRC16 checksum of the first 6 bytes of data

The exception code is a single-byte value indicating the type of error. Several common exception codes defined by the Modbus protocol:

Exception Code	Name	Description
0x01	Illegal Function	The requested function code is not supported
0x02	Illegal Data Address	The requested data address is incorrect
0x03	Illegal Data Value	The requested data value or operation cannot be performed
0x04	Server Failure	Server device failure
0x05	Acknowledge	Request received and processing
0x06	Device Busy	Device is busy and cannot execute the requested operation