5 Ways To Send Data To COM Port From Command Line in Windows

Yes. Windows supports redirecting output to a COM port. Before sending, set the COM port parameters (baud, parity, data bits, stop bits, flow control) with the mode command. Example:

Configure the port:

mode COM3: BAUD=9600 PARITY=N DATA=8 STOP=1

Send text:

echo Hello, device! > COM3

Notes: This sends a text line (with a trailing CR+LF depending on echo). For raw bytes, use the methods below. If you get "Access denied," ensure no other application has the port open and you run the command prompt with appropriate privileges.

Use copy /b to send a binary file directly to the COM port. Example:

Configure the port:

mode COM3: BAUD=115200 PARITY=N DATA=8 STOP=1

Send a file (binary):

copy /b mydata.bin COM3

To send a text file without conversion, use copy /b as well. This method writes the file bytes exactly as-is. To append instead of overwrite, use type myfile >> COM3 only after confirming port behavior.

PowerShell can use the .NET System.IO.Ports.SerialPort class for precise control. Example one-liners and small scripts:

Open, send text, close (one-liner):

powershell -NoProfile -Command "$p=New-Object System.IO.Ports.SerialPort 'COM1',9600,'None',8,one;$p.Open();$p.WriteLine('Hello from PowerShell');$p.Close()"

Send raw bytes from a hex array:

powershell -NoProfile -Command "$p=New-Object System.IO.Ports.SerialPort 'COM3',9600,'None',8,one;$p.Open();$buf=([byte[]] (0x02,0x10,0x03));$p.Write($buf,0,$buf.Length);$p.Close()"

Benefits: full control of baud, parity, and timeouts, and ability to read responses. Use scripts for complex sequences and error handling.

The free RS232Switch utility allows you to configure a COM port and send a small HEX or ASCII command from a single command line. The main advantage is the launching speed, and it works on all Windows operating systems. This program was designed to control AV processors and switches via an RS232 port. If you need to send several messages, you can call this utility from a batch file.

rs232switch.exe [/DEBUG] [/COM 1] [/MODE 9600,8N1] [/ASCII|HEX|HEX2] data_to_send
 /COM - port number (optional, default = 1)
 /MODE - COM port mode (optional, default = baud rate: 9600, data bits: 8, no parity, 1 stop bit)
 /DEBUG - enable debug messages (optional, default = off)
 /ASCII - ASCII characters only
 /HEX - Mixed ASCII and HEX data (default, e.g.: #01data#02)
 /HEX2 - 2-byte HEX data (e.g.: 01020304FF03)

Example: rs232switch /COM 3 /MODE 115200,8N1 #02hello#03

Use third-party tools like Serial Port Monitor. You can send files and data from a command line, and it also has a scripting interface for sending bytes, changing baud rates, and having interactive sessions. This method gives you more flexibility than simple redirection in a command line (e.g., manually configure end of line, hardware handshaking, control characters for software handshaking, define quick commands to send, HEX and ASCII screens, etc.).