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CAT24C128WI-GT3 Arkusz danych(PDF) 4 Page - ON Semiconductor |
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CAT24C128WI-GT3 Arkusz danych(HTML) 4 Page - ON Semiconductor |
4 / 14 page CAT24C128 http://onsemi.com 4 Power−On Reset (POR) The CAT24C128 incorporates Power−On Reset (POR) circuitry which protects the device against powering up in the wrong state. The CAT24C128 will power up into Standby mode after VCC exceeds the POR trigger level and will power down into Reset mode when VCC drops below the POR trigger level. This bi−directional POR feature protects the device against ‘brown−out’ failure following a temporary loss of power. Pin Description SCL: The Serial Clock input pin accepts the Serial Clock generated by the Master. SDA: The Serial Data I/O pin receives input data and transmits data stored in EEPROM. In transmit mode, this pin is open drain. Data is acquired on the positive edge, and is delivered on the negative edge of SCL. A0, A1 and A2: The Address pins accept the device address. When not driven, these pins are pulled LOW internally. WP: The Write Protect input pin inhibits all write operations, when pulled HIGH. When not driven, this pin is pulled LOW internally. Functional Description The CAT24C128 supports the Inter−Integrated Circuit (I2C) Bus data transmission protocol, which defines a device that sends data to the bus as a transmitter and a device receiving data as a receiver. Data flow is controlled by a Master device, which generates the serial clock and all START and STOP conditions. The CAT24C128 acts as a Slave device. Master and Slave alternate as either transmitter or receiver. Up to 8 devices may be connected to the bus as determined by the device address inputs A0, A1, and A2. I2C Bus Protocol The I2C bus consists of two ‘wires’, SCL and SDA. The two wires are connected to the VCC supply via pull−up resistors. Master and Slave devices connect to the 2−wire bus via their respective SCL and SDA pins. The transmitting device pulls down the SDA line to ‘transmit’ a ‘0’ and releases it to ‘transmit’ a ‘1’. Data transfer may be initiated only when the bus is not busy (see A.C. Characteristics). During data transfer, the SDA line must remain stable while the SCL line is HIGH. An SDA transition while SCL is HIGH will be interpreted as a START or STOP condition (Figure 2). The START condition precedes all commands. It consists of a HIGH to LOW transition on SDA while SCL is HIGH. The START acts as a ‘wake−up’ call to all receivers. Absent a START, a Slave will not respond to commands. The STOP condition completes all commands. It consists of a LOW to HIGH transition on SDA while SCL is HIGH. Device Addressing The Master initiates data transfer by creating a START condition on the bus. The Master then broadcasts an 8−bit serial Slave address. The first 4 bits of the Slave address are set to 1010, for normal Read/Write operations (Figure 3). The next 3 bits, A2, A1 and A0, select one of 8 possible Slave devices and must match the state of the external address pins. The last bit, R/W, specifies whether a Read (1) or Write (0) operation is to be performed. Acknowledge After processing the Slave address, the Slave responds with an acknowledge (ACK) by pulling down the SDA line during the 9th clock cycle (Figure 4). The Slave will also acknowledge all address bytes and every data byte presented in Write mode. In Read mode the Slave shifts out a data byte, and then releases the SDA line during the 9th clock cycle. As long as the Master acknowledges the data, the Slave will continue transmitting. The Master terminates the session by not acknowledging the last data byte (NoACK) and by issuing a STOP condition. Bus timing is illustrated in Figure 5. |
Podobny numer części - CAT24C128WI-GT3 |
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Podobny opis - CAT24C128WI-GT3 |
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