Philips Semiconductors
Product specification
USB device with serial interface
PDIUSBD11
I
2
C Interface
The
bus is used to interface to an external microcontroller
needed to control the operation of the USB device. For cost
consideration, the target system microcontroller can be shared and
utilized for both the functional part as well as the USB protocol
interfacing. The PDIUSBD11 implements a slave I
2
C interface.
When the PDIUSBD11 needs to communicate with the
microcontroller it asserts an interrupt signal. The microcontroller
services this interrupt by reading the appropriate status register on
the PDIUSBD11 through the I
2
C bus. (For more information about
the I
2
C serial bus, refer to the
I
2
C Handbook,
Philips order number
9397 750 00013).
The I
2
C interface on the PDIUSBD11 defines two types of
transactions:
I
2
C
Protocol
An I
2
C 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 PDIUSBD11.
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 PDIUSBD11 will send data to the master. The I
2
C-master
must acknowledge all data bytes except the last one. In this way the
I
2
C 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.
•
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.
– 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.
•
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 PDIUSBH11A and the controller.
Timing
The I
2
C interface in the PDIUSBD11 can support clock speeds up to
1 MHz.
ADDRESS TABLE
Type of Address
Command
Data
Physical Address
MSB to LSB
(Binary)
0011 011
0011 010
1999 Jul 22
5
PHILIPS [ NXP SEMICONDUCTORS ]
