A serial loopback test is a troubleshooting procedure used to verify that a serial communication port, adapter, or cable is functioning correctly by routing the transmitted data directly back into the receiver. It isolates the communication hardware and software from external target devices, allowing you to check if the computer can successfully talk to itself before attempting to connect to third-party hardware. How it Works
In normal serial communication, Device A talks to Device B by connecting its Transmit (TX) line to Device B’s Receive (RX) line. In a loopback test, you bridge the TX and RX lines on the same device. When you type or send data through a terminal program, the signal leaves the TX pin, travels through the loopback bridge, and immediately enters the RX pin.
Successful Test: The characters you type or send appear directly on your terminal emulator screen.
Failed Test: Nothing appears on the screen, meaning there is a hardware failure, broken wire, incorrect COM port assignment, or driver issue. Common Hardware Setup (Pinouts)
Depending on your hardware interface, you can perform a loopback test using a jumper wire, a paperclip, or a dedicated loopback plug. Reddit·r/AskElectronics
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