Connecting a USB Track Ball to a device that uses a PS2 connector. Many simple track balls that have a USB A-Male connector will work with a system using the PS2 connectors by using an adaptor that is a USB A-Female on one end and PS2 Male on the other end and plugging it into the mouse port An adapter similar to Digi-Key part number TL1817-ND will make this transition.
Adapters like the one that comes with this mouse, are also available but not sold separately by Digi-Key. Digi-Key part number CH903-ND.
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