The AT43312 is a 5 port USB hub chip supporting one upstream and four downstream ports. The AT43312 connects to an upstream hub or Host/Root Hub via Port0 and the other ports connect to external downstream USB devices. The hub re-transmits the USB differential signal between Port0 and Ports[1:4] in both directions. A USB hub with the AT43312 can operate as a bus-powered or self-powered through chip's power mode configuration pin. The AT43312 is pin- and function-compatible with the AT43311 and can be used as a replacement for the AT43310 with one pin modification. The AT43312 supports the 12 Mb/s full-speed as well as 1.5 Mb/s slow-speed USB transactions. To reduce EMI, the AT43312's oscillator frequency is 6 MHz even though some internal circuitry operates at 48 MHz.