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Difference Between USB Type A and USB Type B Plug/Connector

Updated Jun 14, 2019

Reported In


  • USB-232
  • USB-232/2
  • USB-232/4
  • USB-485
  • USB-485/4
  • USB-485/2
  • Serial Interface Device

Issue Details

In the Catalog for USB-232/485 Series Interfaces, it says that the 1-port interface has a USB Type A plug whereas the 2- and 4-port interfaces have a USB Type B connector. What is the difference? Do I need any additional hardware to connect either one to my computer?


USB Type A and USB Type B plugs have the same number of pins and are electrically identical. They are only different mechanically. This was an intentional feature designed by the USB Implementers Forum to prevent connecting a host to another host, which could cause a short circuit. 

In the following figure, the type A plug is on the left and the type B plug is shown on the right. Notice the pin numbering as well. Each plug type has the same number of pins, they are only different in mechanical design. 

Additional Information

The USB receptacle on your PC is a type A connector and can be recognized by its rectangular shape. Type A receptacles can be found on upstream devices such as a USB host, or a hub. Type A plugs can be found on cables, and smaller peripherals such as a mouse and a flash drive. 

However, many larger USB peripherals such as printers and scanners use a detachable cable, and use the Type B receptacle, which has a square shape. Instruments are another type of downstream device. To connect an instrument to your PC, you will need to use a USB Type A to Type B cable.


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