PS/2 to USB keyboard adaptor supporting N-key rollover

摘要

A USB converter circuit for converting electrical signals from a key scan circuit (in PS/2 or other formats) into USB signals for a computer while supporting N-key rollover (NKRO) functions. The converter circuit can be implemented as a stand-alone PS/2 to USB keyboard converter or as an integral component of a USB keyboard or KVM switch. The converter circuit includes a converter module that generates keyboard data packets in the USB format having a 16-byte, 64-byte, etc. format representing key press information for up to 8 modifier keys and 14, 62, etc. non-modifier keys, respectively. The converter circuit also includes a USB device controller module which transmits the 16-byte etc. USB keyboard data as one or multiple USB data packets to the host computer. When multiple USB data packets are needed to transmit each keyboard data packet (depending on the USB speed), they are transmitted in consecutive polling periods.