The Am79C989 Quad Ethernet Switching Transceiver (QuESTTM) is a four-port physical layer (PHY) device that provides all of the analog functions needed for a 10BASE-T switch, including four independent Manchester Encode/Decode units (MENDECs) and four independent 10BASE-T transceivers. If the AUI p o rt i s u s e d fo r a 1 0 B A S E - 2 , 1 0 B A S E - 5 , o r 10BASE-FL transceiver, one of the four 10BASE-T ports is disabled.