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PCA9500

8-bit I2C-bus and SMBus I/O port with 2-kbit EEPROM

NXP Semiconductors. 

NXP Semiconductors

PCA9500

8-bit I2C-bus and SMBus I/O port with 2-kbit EEPROM

8. 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.

8.1 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 15).

SDA

SCL

Fig 15. Bit transfer

data line

stable;

data valid

change

of data

allowed

mba607

8.1.1 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 16).

SDA

SCL

S

START condition

Fig 16. Definition of START and STOP conditions

P

STOP condition

mba608

PCA9500_4

Product data sheet

Rev. 04 — 15 April 2009

© NXP B.V. 2009. All rights reserved.

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