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What is the Difference between USB Type A and USB Type B Plug/Connector?

Hardware: Serial>>RS-232

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?

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

The two types of 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 image, 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. For more information, see the Related Links section.

Related Links:
White Paper: The Future for New Bus Technologies in Instrument Control and Connectivity
White Paper: Six Things You Need to Know about USB Control
External Link: Universal Serial Bus -


Report Date: 10/07/2003
Last Updated: 04/20/2015
Document ID: 326BPC5L

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