Modbus RTU PWM Input 8CH User Guide

Hardware Description

Product Parameters

Parameter	Specification
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
Pulse Input Voltage Range	3.3 V ~ 30 V
Pulse Frequency Measurement Range	400 Hz ~ 50 kHz
Pulse Resolution	0.01 Hz
Pulse Accuracy	5‰
Duty Cycle Measurement Range	0 ~ 100 %
Duty Cycle Resolution	0.01 %
Duty Cycle Accuracy	5 ‰

Indicator Light Description

Indicator Light	Status Description
STATUS LED	MCU indicator, flashes when the MCU is operating normally
TXD LED	Transmission indicator, lights up when data is being sent
RXD LED	Reception indicator, lights up when data is being received

Hardware Description

CHN+ is the positive input, CHN- is the negative input. The PWM measurement frequency range is 400 Hz ~ 50 kHz, and the duty cycle range is 0 ~ 100%.

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, it will return the 8-channel pulse input data.
```
01 04 00 00 00 18
```

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, send the following command to query channel 2 pulse input data.
```
01 04 00 03 00 03
```

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. Select the actual device address for Slave ID, 04 Read Input Registers (3x) for Function, and 24 for Quantity. 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 a successful connection, the register data will be displayed. For ease of observation, you need to set the frequency format. Select registers 1, 3, 6, 9, 12, 15, 18, 21, right-click and choose Format -> 32 Bit Unsigned -> Big-endian to set the format to unsigned 32-bit big-endian. You can also add register notes in the Alias column.
After setting the correct format, the 8-channel pulse frequency and duty cycle are displayed normally as shown below.

Development Protocol

Function Code Introduction

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

Register Address Description

Address (HEX)	Register Content	Register Value	Access	Modbus Function Code
3x0000 3x0001	Channel 1 Frequency High 16 bits Channel 1 Frequency Low 16 bits	Unsigned 32-bit value, unit 0.01 Hz, range: 40000 ~ 5000000, i.e., 400 Hz ~ 50 kHz	Read	0x04
3x0002	Channel 1 Duty Cycle	Value is unsigned 16-bit hexadecimal, unit 0.01%, range 0~10000, i.e., 0~100%	Read	0x04
3x0003 3x0004	Channel 2 Frequency High 16 bits Channel 2 Frequency Low 16 bits	Unsigned 32-bit value, unit 0.01 Hz, range: 40000 ~ 5000000, i.e., 400 Hz ~ 50 kHz	Read	0x04
3x0005	Channel 2 Duty Cycle	Value is unsigned 16-bit hexadecimal, unit 0.01%, range 0~10000, i.e., 0~100%	Read	0x04
3x0006 3x0007	Channel 3 Frequency High 16 bits Channel 3 Frequency Low 16 bits	Unsigned 32-bit value, unit 0.01 Hz, range: 40000 ~ 5000000, i.e., 400 Hz ~ 50 kHz	Read	0x04
3x0008	Channel 3 Duty Cycle	Value is unsigned 16-bit hexadecimal, unit 0.01%, range 0~10000, i.e., 0~100%	Read	0x04
3x0009 3x000A	Channel 4 Frequency High 16 bits Channel 4 Frequency Low 16 bits	Unsigned 32-bit value, unit 0.01 Hz, range: 40000 ~ 5000000, i.e., 400 Hz ~ 50 kHz	Read	0x04
3x000B	Channel 4 Duty Cycle	Value is unsigned 16-bit hexadecimal, unit 0.01%, range 0~10000, i.e., 0~100%	Read	0x04
3x000C 3x000D	Channel 5 Frequency High 16 bits Channel 5 Frequency Low 16 bits	Unsigned 32-bit value, unit 0.01 Hz, range: 40000 ~ 5000000, i.e., 400 Hz ~ 50 kHz	Read	0x04
3x000E	Channel 5 Duty Cycle	Value is unsigned 16-bit hexadecimal, unit 0.01%, range 0~10000, i.e., 0~100%	Read	0x04
3x000F 3x0010	Channel 6 Frequency High 16 bits Channel 6 Frequency Low 16 bits	Unsigned 32-bit value, unit 0.01 Hz, range: 40000 ~ 5000000, i.e., 400 Hz ~ 50 kHz	Read	0x04
3x0011	Channel 6 Duty Cycle	Value is unsigned 16-bit hexadecimal, unit 0.01%, range 0~10000, i.e., 0~100%	Read	0x04
3x0012 3x0013	Channel 7 Frequency High 16 bits Channel 7 Frequency Low 16 bits	Unsigned 32-bit value, unit 0.01 Hz, range: 40000 ~ 5000000, i.e., 400 Hz ~ 50 kHz	Read	0x04
3x0014	Channel 7 Duty Cycle	Value is unsigned 16-bit hexadecimal, unit 0.01%, range 0~10000, i.e., 0~100%	Read	0x04
3x0015 3x0016	Channel 8 Frequency High 16 bits Channel 8 Frequency Low 16 bits	Unsigned 32-bit value, unit 0.01 Hz, range: 40000 ~ 5000000, i.e., 400 Hz ~ 50 kHz	Read	0x04
3x0017	Channel 8 Duty Cycle	Value is unsigned 16-bit hexadecimal, unit 0.01%, range 0~10000, i.e., 0~100%	Read	0x04
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

Command Operation Introduction

Read Pulse Input Command

Transmission Code: 01 04 00 00 00 03 B0 0B

Field	Description	Note
01	Device Address	0x00 indicates broadcast address; 0x01-0xFF indicate device address
04	04 Command	Read Input Registers
00 00	Register Start Address	Starting register for channel read. Each channel occupies three registers: first two store frequency, last stores duty cycle
00 03	Number of Registers	Number of registers to read, cannot exceed maximum register count
B0 0B	CRC16	CRC16 checksum of the first 6 bytes of data

Return Code: 01 04 06 00 3B 83 A5 03 01 7D C1

Field	Description	Note
01	Device Address	0x00 indicates broadcast address; 0x01-0xFF indicate device address
04	04 Command	Read Input Registers
06	Byte Count	Data length
3B 83 A5 03 03 01	Register Data Frequency High 16-bit Frequency Low 16-bit Duty Cycle	Each channel occupies three registers: first two store frequency, last stores duty cycle Frequency is unsigned 32-bit hexadecimal, unit 0.01 Hz, range: 40000~5000000 (400 Hz ~ 50 kHz) Duty cycle: unsigned 16-bit, unit 0.01%, range 0~10000 (0~100%)
7D C1	CRC16	CRC16 checksum of the first 6 bytes of data

Example: Device with address 1

Read channels 1-8 : 01 04 00 00 00 18 F0 00
Read channel 2 : 01 04 00 03 00 03 40 0B
Read channels 3-5 : 01 04 00 06 00 09 D0 0D
Read channel 1 : 01 04 00 00 00 03 B0 0B
Return: 01 04 06 00 00 9C 40 13 88 42 41 //Channel 1, 400 Hz, 50% duty cycle

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 Codes

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