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Philips Semiconductors
ISP1122
USB stand-alone hub
Product specification Rev. 03 — 29 March 2000 9 of 48
9397 750 07002
© Philips Electronics N.V. 2000. All rights reserved.
6.2 Philips Serial Interface Engine (SIE)
The Philips SIE implements the full USB protocol layer. It is completely hardwired for
speed and needs no firmware intervention. The functions of this block include:
synchronization pattern recognition, parallel/serial conversion, bit (de-)stuffing, CRC
checking/generation, Packet IDentifier (PID) verification/generation, address
recognition, handshake evaluation/generation.
6.3 Hub repeater
The hub repeater is responsible for managing connectivity on a ‘per packet’ basis. It
implements ‘packet signalling’ and ‘resume’ connectivity. Low-speed devices can be
connected to downstream ports. If a low-speed device is detected the repeater will
not propagate upstream packets to the corresponding port, unless they are preceded
by a PREAMBLE PID.
6.4 End-of-frame timers
This block contains the specified EOF1 and EOF2 timers which are used to detect
‘loss-of-activity’ and ‘babble’ error conditions in the hub repeater. The timers also
maintain the low-speed keep-alive strobe which is sent at the beginning of a frame.
6.5 General and individual port controller
The general and individual port controllers together provide status and control of
individual downstream ports. Any port status change will be reported to the host via
the hub status change (interrupt) endpoint.
6.6 GoodLink
Indication of a good USB connection is provided through GoodLink technology. An
LED can be directly connected via an external 330 Ω resistor.
During enumeration the LED blinks on momentarily. After successful configuration of
the ISP1122, the LED is permanently on. The LED blinks off for 100 ms upon each
successful packet transfer (with ACK). The hub GoodLink indicator blinks when the
hub receives a packet addressed to it. Downstream GoodLink indicators blink upon
an acknowledgment from the associated port. In ‘suspend’ mode the LED is off.
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.
6.7 Bit clock recovery
The bit clock recovery circuit recovers the clock from the incoming USB data stream
using a 4× oversampling principle. It is able to track jitter and frequency drift as
specified by the
USB Specification Rev. 1.1
.
6.8 Voltage regulator
A 5 to 3.3 V DC-DC regulator is integrated on-chip to supply the analog transceiver
and internal logic. This can also be used to supply the terminal 1.5 kΩ pull-up resistor
on the D+ line of the upstream connection.