Philips Semiconductors ISP1521
Hi-Speed USB hub controller
Product data Rev. 03 — 24 November 2004 11 of 53
9397 750 13702 © Koninklijke Philips Electronics N.V. 2004. All rights reserved.
8.2.5 Hub repeater
A hub repeater is responsible for managing connectivity on a per packet basis. It
implements packet signaling connectivity and resume connectivity. There are two
repeaters in the ISP1521: a Hi-Speed USB repeater and an Original USB repeater.
The only major difference between these two repeaters is the speed at which they
operate. When the hub is connected to an Original USB system, it automatically
switches itself to function as a pure Original USB hub.
8.2.6 Hub and port controllers
The hub controller provides status report. The port controller provides control for
individual downstream facing port; it controls the port routing module. Any port status
change will be reported to the host via the hub status change (interrupt) endpoint.
8.2.7 Bit clock recovery
The bit clock recovery circuit extracts the clock from the incoming USB data stream.
8.3 Phase-locked loop clock multiplier
A 12 MHz to 480 MHz clock multiplier PLL is integrated on-chip. This allows the use
of low-cost 12 MHz crystals. The low crystal frequency also minimizes
ElectroMagnetic Interference (EMI). No external components are required for the
operation of the PLL.
8.4 I2C-bus controller
A simple serial I2C-bus interface is provided to transfer vendor ID, product ID and
string descriptor from an external I2C-bus EEPROM (forexample, Philips PCF8582 or
equivalent) or microcontroller. A master/slave I2C-bus protocol is implemented
according to the timing requirements as mentioned in the I2C-bus standard
specifications. The maximum data count during I2C-bus transfers for theISP1521 is
256 bytes.
8.5 Overcurrent detection circuit
An overcurrent detection circuit is integrated on-chip.The main features of this circuit
are: self reporting, automatic resetting, low-trip time and low cost. This circuit offers
an easy solution at no extra hardware cost on the board.
8.6 GoodLink
Indication of a good USB connection is provided through GoodLink technology. An
LED can be directly connected to pin HUBGL_N via an external 330 Ω resistor.
During enumeration, the LED blinks on momentarily. After successful configuration,
the LED blinks off for 100 ms upon each transaction.
This feature provides a user-friendly indication of the status of the hub,the connected
downstream devices and the USB traffic.It is a useful diagnostics tool to isolate faulty
USB equipment and helps to reduce field support and hotline costs.
8.7 Power-on reset
The ISP1521 has an internal Power-On Reset (POR) circuit.