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CAT5221YI-00 Datasheet(PDF) 6 Page - ON Semiconductor |
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CAT5221YI-00 Datasheet(HTML) 6 Page - ON Semiconductor |
6 / 16 page CAT5221 Doc. No. MD-2113 Rev. L 6 © 2008 SCILLC. All rights reserved. Characteristics subject to change without notice SERIAL BUS PROTOCOL The following defines the features of the I 2C bus protocol: (1) Data transfer may be initiated only when the bus is not busy. (2) During a data transfer, the data line must remain stable whenever the clock line is high. Any changes in the data line while the clock is high will be interpreted as a START or STOP condition. The device controlling the transfer is a master, typically a processor or controller, and the device being controlled is the slave. The master will always initiate data transfers and provide the clock for both transmit and receive operations. Therefore, the CAT5221 will be considered a slave device in all applications. START Condition The START Condition precedes all commands to the device, and is defined as a HIGH to LOW transition of SDA when SCL is HIGH. The CAT5221 monitors the SDA and SCL lines and will not respond until this condition is met. STOP Condition A LOW to HIGH transition of SDA when SCL is HIGH determines the STOP condition. All operations must end with a STOP condition. DEVICE ADDRESSING The bus Master begins a transmission by sending a START condition. The Master then sends the address of the particular slave device it is requesting. The four most significant bits of the 8-bit slave address are fixed as 0101 for the CAT5221 (see Figure 5). The next four significant bits (A3, A2, A1, A0) are the device address bits and define which device the Master is accessing. Up to sixteen devices may be individually addressed by the system. Typically, +5V and ground are hard-wired to these pins to establish the device's address. After the Master sends a START condition and the slave address byte, the CAT5221 monitors the bus and responds with an acknowledge (on the SDA line) when its address matches the transmitted slave address. Acknowledge After a successful data transfer, each receiving device is required to generate an acknowledge. The Acknowledging device pulls down the SDA line during the ninth clock cycle, signaling that it received the 8 bits of data. The CAT5221 responds with an acknowledge after receiving a START condition and its slave address. If the device has been selected along with a write operation, it responds with an acknowledge after receiving each 8-bit byte. When the CAT5221 is in a READ mode it transmits 8 bits of data, releases the SDA line, and monitors the line for an acknowledge. Once it receives this acknowledge, the CAT5221 will continue to transmit data. If no acknowledge is sent by the Master, the device terminates data transmission and waits for a STOP condition. Figure 4. Acknowledge Timing ACKNOWLEDGE 1 START SCL FROM MASTER 89 DATA OUTPUT FROM TRANSMITTER DATA OUTPUT FROM RECEIVER |
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