The ISP1123 is a compound Universal Serial Bus (USB) hub device which complies with USB Specification Rev. 1.1. It integrates a Serial Interface Engine (SIE), hub repeater, hub controller, USB data transceivers and a 3.3 V voltage regulator. It has a configurable number of downstream ports, ranging from 2 to 5, with one port dedicated to an embedded or non-removable function. The ISP1123 can be bus-powered, self-powered or hybrid-powered. When it is hybrid-powered the hub functions are powered by the upstream power supply (VBUS), but the downstream ports are powered by an external 5 Volt supply. The low power consumption in `suspend' mode allows easy design of equipment that is compliant with the ACPITM, OnNowTM and USB power management requirements. The ISP1123 has built-in overcurrent sense inputs, supporting individual and ganged mode overcurrent protection for downstream ports. All ports (including the hub) have GoodLinkTM indicator outputs for easy visual monitoring of USB traffic. The ISP1123 has a serial I2C-bus interface for external EEPROM access and a reduced frequency (6 MHz) crystal oscillator. These features allow significant cost savings in system design and easy implementation of advanced USB functionality into PC peripherals. c