Philips Universal Serial Bus ISP1122 - Manual (Page 8)

Philips Semiconductors
ISP1122
USB stand-alone hub
Product specification Rev. 03 — 29 March 2000 8 of 48
9397 750 07002 © Philips Electronics N.V. 2000. All rights reserved.
[1] Symbol names with an overscore (e.g. NAME) indicate active LOW signals.
[2] The voltage at pin V
reg(3.3)
is gated by the RESET pin. This allows fully self-powered operation by
connecting RESET to V
BUS
(+5 V USB supply). If V
BUS
is lost upstream port D+ will not be driven.
[3] See Table 4 “Mode selection” .
[4] To disable a downstream port connect both D
+
and D
−
to V
CC
via a 1 M
Ω
resistor; unused ports must
be disabled in reverse order starting from port 5.
[5] Analog detection circuit can be switched off using an external EEPROM, see Table 23 ; in this case,
the pin functions as a logic input (TTL level).
[6] Downstream ports 1 and 2 cannot be disabled.
6. Functional description
The ISP1122 is a stand-alone USB hub with up to 5 downstream ports. The number
of ports can be configured between 2 and 5. The downstream ports can be used to
connect low-speed or full-speed USB peripherals. All standard USB requests from
the host are handled by the hardware without the need for firmware intervention. The
block diagram is shown in
Figure 1 .
The ISP1122 requires only a single supply voltage. An internal 3.3 V regulator
provides the supply voltage for the analog USB data transceivers.
The ISP1122 supports both bus-powered and self-powered hub operation. When
using bus-powered operation a downstream port cannot supply more than 100 mA to
a peripheral. In case of self-powered operation an external supply is used to power
the downstream ports, allowing a current consumption of max. 500 mA per port.
A basic I 2 C-bus interface is provided for reading vendor ID, product ID and
configuration bits from an external EEPROM upon a reset.
6.1 Analog transceivers
The integrated transceiver interfaces directly to the USB cables through external
termination resistors. They are capable of transmitting and receiving serial data at
both ‘full-speed’ (12 Mbit/s) and ‘low-speed’ (1.5 Mbit/s) data rates. The slew rates
are adjusted according to the speed of the device connected and lie within the range
mentioned in the
USB Specification Rev. 1.1.
DM2 26 AI/O downstream port 2 D
−
connection (analog) [6]
DP2 27 AI/O downstream port 2 D
+
connection (analog) [6]
PSW1/GL1 [3] 28 O modes 4 to 6: power switch control output for downstream
port 1 (open-drain, 6 mA)
modes 0 to 3, 7: GoodLink LED indicator output for
downstream port 1 (open-drain, 6 mA); to connect an LED
use a 330
Ω
series resistor
Table 3: Pin description for LQFP32 …continued
Symbol [1] Pin Type Description