如何在PowerShell中向串口写入255？写入超127值时输出恒为63

Ah, I get exactly what's happening here—this is an encoding problem plain and simple. Let's break it down:

Why You're Seeing 63 Instead of 255 #

By default, the SerialPort object in PowerShell uses ASCII encoding. ASCII only supports values from 0 to 127. Any value above 127 gets replaced with ASCII character 63 (the question mark ?), because ASCII doesn't recognize those extended values. That's why 127 works fine (it's the valid DEL character in ASCII) but 255 gets turned into 63.

Two Reliable Fixes #

1. Use a Single-Byte Encoding That Supports 0-255

Instead of sticking with ASCII, switch to an encoding that handles the full 0-255 byte range. Latin1 (ISO-8859-1) is perfect for this—it maps each byte directly to a character without replacement.

Here's how to implement it:

# Initialize the serial port (adjust COM port, baud rate to match your setup)
$port = New-Object System.IO.Ports.SerialPort "COM3", 9600, None, 8, One

# Set encoding to Latin1 (supports 0-255 values)
$port.Encoding = [System.Text.Encoding]::GetEncoding(28591)

$port.Open()
# Write value 255 as a char
$port.Write([char]255, 0, 1)
$port.Close()

2. Write Directly as a Byte Array (Most Reliable)

Since serial ports work with raw bytes, bypassing encoding entirely is the safest approach. This way you're sending exactly the byte you want, no conversion involved.

Try this code:

# Initialize serial port
$port = New-Object System.IO.Ports.SerialPort "COM3", 9600, None, 8, One

$port.Open()
# Create a byte array with your value (255)
$byteToSend = [byte]255
$port.Write([byte[]]@($byteToSend), 0, 1)
$port.Close()

Quick Check #

Make sure your serial port settings (baud rate, data bits, stop bits, parity) match whatever device you're communicating with. Mismatched settings can also cause weird data corruption, even if you fix the encoding.

内容的提问来源于stack exchange，提问作者Spectrum