A USB-to-TTL adapter (also called USB-to-UART adapter or USB-to-UART bridge) is a simple USB device that lets you connect a device with TTL/UART port to your PC through the regular USB port. It can be used to update firmware on routers, modems, mobile phones, hard disks and so on. If you have bought a new USB-to-TTL adapter from some online store, then first thing you should do is check if it is working properly. We have already covered a detailed article on how you can test your USB-to-TTL adapter using a third party program called uCon. But uCon has its limitations, for example, you cannot set any desired baud-rate for serial connections and you are forced to use only pre-specified baud-rates.
Instead of using uCon, you can use Putty to run the loopback test on your USB-to-TTL adapter. Putty is open source, offers more functions and you can set any desired baud rate you want to. Here is how you can test your USB-to-TTL adapter using Putty:
- Use any jumper wire and connect the RXD pin to the TXD pin of your USB-to-TTL adapter. Depending on the adapter, the pins could be labeled RX and TX or RXI, TXO etc. Attach it in to one of the USB ports of your Windows PC.
- Press Win+R to open the Run dialog, type devmgmt.msc in it and press Enter.
- In the Device Manager, expand Ports (COM & LPT) and check the port number assigned to your USB-to-TTL adapter. On my computer, it turned out to be COM22 as can be seen from the following picture:
- Download Putty (it is portable software, so no need of installing it) and launch it.
- Select Serial from the type of connections. Type in the COM port (the port we found in step 3 above) and select a baud-rate speed (you can let it be 9600). Click on the Open button to start the connection.
- A new console window shall open up. Here you can type anything you like. For a working loopback connection, whatever you type should be returned back to you and you should see whatever you are typing (as if you are typing in a text editor).
- For a faulty adapter, you will not see anything you type in the Putty connection window.
Conclusion: Putty can be used for testing any USB to TTL adapter easily through the loopback test. This is a great way to check whether your USB to TTL adapter is faulty or not.