PCA9557D 查看數據表（PDF） - Philips Electronics

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PCA9557D

8-bit I2C and SMBus I/0 port with reset

Philips Electronics 

Philips Semiconductors

8-bit I2C and SMBus I/0 port with reset

Product data

PCA9557

CHARACTERISTICS OF THE I2C-BUS

The I2C-bus is for 2-way, 2-line communication between different ICs

or modules. The two lines are a serial data line (SDA) and a serial

clock line (SCL). Both lines must be connected to a positive supply

via a pull-up resistor when connected to the output stages of a device.

Data transfer may be initiated only when the bus is not busy.

Bit transfer

One data bit is transferred during each clock pulse. The data on the

SDA line must remain stable during the HIGH period of the clock

pulse as changes in the data line at this time will be interpreted as

control signals (see Figure 8).

Start and stop conditions

Both data and clock lines remain HIGH when the bus is not busy. A

HIGH-to-LOW transition of the data line, while the clock is HIGH is

defined as the start condition (S). A LOW-to-HIGH transition of the

data line while the clock is HIGH is defined as the stop condition (P)

(see Figure 9).

System configuration

A device generating a message is a ‘transmitter’, a device receiving

is the ‘receiver’. The device that controls the message is the

‘master’ and the devices which are controlled by the master are the

‘slaves’ (see Figure 10).

SDA

SCL

data line

stable;

data valid

change

of data

allowed

SW00363

Figure 8. Bit transfer

SDA

SDA

SCL

S

SCL

P

START condition

STOP condition

Figure 9. Definition of start and stop conditions

SW00365

SDA

SCL

MASTER

TRANSMITTER/

RECEIVER

SLAVE

RECEIVER

SLAVE

TRANSMITTER/

RECEIVER

MASTER

TRANSMITTER

MASTER

TRANSMITTER/

RECEIVER

SLAVE

Figure 10. System configuration

I2C

MULTIPLEXER

SW00366

2001 Dec 12

7

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