PDIUSBH12 datasheet(9/28 Pages) PHILIPS

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Philips Semiconductors

Product specification

PDIUSBH12

USB 2-port hub

1999 Jul 22

APPLICATION DIAGRAM

I2C

GOODLINK

™ LED

POWER SWITCH

AND

OVERCURRENT CIRCUIT

SWITCHED

H12

µC

CLKOUT

12MHz

USB

DOWNSTREAM

USB

UPSTREAM

3.3V

SV00853

I2C Interface

The I2C bus is used to interface to an external microcontroller

needed to control the operation of the hub. For cost consideration,

the target system microcontroller can be shared and utilized for this

purpose. The PDIUSBH12 implements a slave I2C interface. When

the PDIUSBH12 needs to communicate with the microcontroller it

asserts an interrupt signal. The microcontroller services this interrupt

by reading the appropriate status register on the PDIUSBH12

through the I2C bus. (For more information about the I2C serial bus,

refer to the

I2C Handbook, Philips order number 9397 750 00013).

The I2C interface on the PDIUSBH12 defines two types of

transactions:

1. command transaction

A command transaction is used to define which data (e.g., status

byte, buffer data, ...) will be read from / written to the USB

interface in the next data transaction. A data transaction usually

follows a command transaction.

2. data transaction

A data transaction reads data from / writes data to the USB

interface. The meaning of the data is dependent on the

command transaction which was sent before the data

transaction.

Two addresses are used to differentiate between command and

data transactions. Writing to the command address is interpreted as

a command, while reading from / writing to the data address is used

to transfer data between the PDIUSBH12 and the controller.

ADDRESS TABLE

TYPE OF ADDRESS

PHYSICAL ADDRESS

(MSB to LSB)

Command

0011 011 (binary)

Data

0011 010 (binary)

Protocol

An I2C transaction starts with a ‘Start Condition’, followed by an

address. When the address matches either the command or data

address the transaction starts and runs until a ‘Stop Condition’ or

another ‘Start Condition’ (repeated start) occurs.

The command address is write-only and is unable to do a read. The

next bytes in the message are interpreted as commands. Several

command bytes can be sent after one command address. Each of

the command bytes is acknowledged and passed on to the Memory

Management Unit inside the PDIUSBH12.

When the start condition address matches the data address, the

next bytes are interpreted as data. When the RW bit in the address

indicates a ‘master writes data to slave’ (=‘0’) the bytes are received,

acknowledged and passed on to the Memory Management Unit. If

the RW bit in the address indicates a ‘master reads data from slave’

(=‘1’) the PDIUSBH12 will send data to the master. The I2C-master

must acknowledge all data bytes except the last one. In this way the

I2C interface knows when the last byte has been transmitted and it

then releases the SDA line so that the master controller can

generate the STOP condition.

Repeated start support allows another packet to be sent without

generating a Stop Condition.

Timing

The I2C interface in the PDIUSBH12 can support clock speeds up to

1MHz.

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