ISP1123 datasheet(21/49 Pages) PHILIPS

21 / 49 page

Philips Semiconductors

ISP1123

USB compound hub

Preliminary speciﬁcation

Rev. 01 — 5 October 1999

21 of 49

9397 750 06325

11. I2C-bus interface

A simple I2C-bus interface is provided in the ISP1123 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.

11.1 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.

11.2 Hardware connections

Via the I2C-bus interface the ISP1123 can be connected to an external EEPROM

(PCF8582 or equivalent). The hardware connections are shown in Figure 6.

The SCL and SDA pins are multiplexed with pins OPTION and INDV respectively.

Fig 6.

EEPROM connection diagram.

idth

MBL081

INDV/SDA

OPTION/SCL

SDA

SCL

VDD

ISP1123

USB HUB

PCF8582

EEPROM

equivalent

I2C-bus

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