Philips Universal Serial Bus ISP1122 - Manual (Page 20)

Philips Semiconductors
ISP1122
USB stand-alone hub
Product specification Rev. 03 — 29 March 2000 20 of 48
9397 750 07002 © Philips Electronics N.V. 2000. All rights reserved.
9.4.6 Get configuration descriptor
The hub returns 25 bytes containing the configuration descriptor (9 bytes, see
Table 11 ), the interface descriptor (9 bytes, see Table 12 ) and the endpoint descriptor
(7 bytes, see Table 13 ).
9.4.7 Get device descriptor
The hub returns 18 bytes containing the device descriptor, see Table 10 .
9.4.8 Get hub descriptor
The hub returns 9 bytes containing the hub descriptor, see Table 14 .
9.4.9 Get string descriptor (0)
The hub returns 4 bytes containing the language ID, see Table 15 .
9.4.10 Get string descriptor (1)
The hub returns 46 bytes containing the manufacturer name, see Table 15 .
9.4.11 Get string descriptor (2)
The hub returns 16 bytes containing the product name, see Table 15 .
10. I 2 C-bus interface
A simple I 2 C-bus interface is provided in the ISP1122 to read customized vendor ID,
product ID and some other configuration bits from an external EEPROM. The
interface supports single master operation at a nominal bus speed of 93.75 kHz.
The I 2 C-bus interface is intended for bidirectional communication between ICs via two
serial bus wires, SDA (data) and SCL (clock). Both lines are driven by open-drain
circuits and must be connected to the positive supply voltage via pull-up resistors.
10.1 Protocol
The I 2 C-bus protocol defines the following conditions:
• Bus free: both SDA and SCL are HIGH
• START: a HIGH-to-LOW transition on SDA, while SCL is HIGH
• STOP: a LOW-to-HIGH transition on SDA, while SCL is HIGH
• Data valid: after a START condition, data on SDA are stable during the HIGH
period of SCL; data on SDA may only change while SCL is LOW.
Each device on the I 2 C-bus has a unique slave address, which the master uses to
select a device for access.
The master starts a data transfer using a START condition and ends it by generating
a STOP condition. Transfers can only be initiated when the bus is free. The receiver
must acknowledge each byte by means of a LOW level on SDA during the ninth clock
pulse on SCL.
For detailed information please consult The I 2 C-bus and how to use it., order number
9398 393 40011.