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ISP1123BD

Universal Serial Bus compound hub

Philips Electronics 

Philips Semiconductors

ISP1123

USB compound hub

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.

9397 750 06325

Preliminary specification

idth

VDD

VDD

OPTION/SCL

INDV/SDA

ISP1123

USB HUB

RP

RP

I2C-bus

Fig 6. EEPROM connection diagram.

Rev. 01 — 5 October 1999

SCL

A0

SDA

A1

PCF8582 A2

EEPROM

or

equivalent

MBL081

© Philips Electronics N.V. 1999. All rights reserved.

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