Serial communication acquisition

Reads and writes local serial ports using specified communication formats.

1. Create nodes

(1) Open CommBridge Digital Twin and switch to Device Connectivity.

(2) Drag Serial Communication, Data Processing, and MQTT Upload into the workspace to create three nodes.

(3) Connect Serial Communication → Data Processing → MQTT Upload.

2. Create a scheme

(1) Double-click Serial Communication and select Add scheme.

(2) Enter connection settings and select Next.

(3) Select Add configuration, enter the settings, and confirm.

(4) Select Next to open data frame parsing.

(5) Select Add parser, enter point configuration, and confirm.

(6) Select Finish to add the acquisition scheme.

(7) Enable the scheme and select Save.

3. View results

(1) Select Deploy under Device Connectivity and wait for success.

(2) Switch to Digital Twin and hover over Serial Communication to display node information.

(3) Select a scheme to view real-time and historical point data in its groups.

Acquired real-time values are hexadecimal.

4. Configuration reference

Connection settings

Parameter	Description	Format	Example	Notes
Scheme name	User-defined scheme name	Nonempty	Temperature/humidity acquisition
Interface	Actual serial interface on the device	ttyS0, ttyS1	ttyO3	Usually RS485; depends on USB connection order
Data bits	Number of data bits in each unit	7, 8	8
Stop bits	Marks the end of a packet	1, 2	1
Parity	Simple serial error checking	Odd, Even, or None	None
Baud rate	Symbols transmitted per second	11520, 57600, 38400, 19200, 9600, or 4800	19200

Data frame configuration

Parameter	Prerequisite	Description	Format	Example	Notes
Name		User-defined name	Nonempty; cannot start with a digit or contain . , [ ] { } ( ) ; =	Distance group 1
Frame mode		Data frame transmission mode	HEX, ASCII	HEX	ASCII is rarely used
Frame format	Depends on frame mode	Regex: ^(?:[0-9a-fA-F]{2} )*[0-9a-fA-F]{2}$	Space-separated hexadecimal string	0f 03 00 00 00 01 85 24
Cycle time (ms)			Number	1000
Enabled		If disabled, it cannot appear or be configured in frame parsing	disabled, enabled	enabled

Note: Serial can read only 20 data items at a time.

Data frame parsing

Parameter	Description	Format	Example	Notes
Name	User-defined name	Nonempty	H
Parsing			byte[3]byte[4]
Enabled	If disabled, it cannot appear or be configured in frame parsing	disabled, enabled	enabled

5. Serial protocol parameter details

Frame modes:

• HEX: hexadecimal, using 16 characters from 0 to F.
• ASCII: a character set representing 128 characters.

ASCII and Hex differ primarily in the range of characters they represent.

The following HEX request is a Modbus RTU example for reading holding registers (function code 0x03):

Device address [1 byte]	Function code [1 byte]	Start address [2 bytes]	Register count [2 bytes]	CRC [2 bytes]
address	03	AddrH AddrL	NumH NumL	CRCL CRCH

CRC (cyclic redundancy check) uses CRC-16/MODBUS with polynomial X16+X15+X2+1. The checksum low byte is transmitted first.

Example: 01 03 00 10 00 01 85 CF

Command	01	03	00	10	00	01	85	CF
Meaning	Device address	Read command	Register start address high byte	Register start address low byte	Read quantity high byte	Read quantity low byte	CRCL	CRCH

The following is a Modbus ASCII request for reading holding registers (function code 0x03). Each raw byte is encoded as two ASCII hexadecimal characters. The table excludes the starting colon (:) and ending CR/LF characters:

Device address [2 characters]	Function code [2 characters]	Start address [4 characters]	Register count [4 characters]	LRC [2 characters]
address	03	AddrH AddrL	NumH NumL	Two hexadecimal characters of the LRC

LRC (longitudinal redundancy check) sums the raw address, function-code, and data bytes, discards carries beyond 8 bits, and takes the two’s complement to produce a one-byte checksum. The starting colon (:) and ending CR/LF are excluded.