ISP1122ABD datasheet(20/48 Pages) PHILIPS

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Philips Semiconductors

ISP1122A

USB stand-alone hub

Preliminary speciﬁcation

Rev. 01 — 27 March 2000

20 of 48

9397 750 06986

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. I2C-bus interface

A simple I2C-bus interface is provided in the ISP1122A 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 I2C-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 I2C-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 I2C-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 I2C-bus and how to use it., order number

9398 393 40011.

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