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CY14ME064J Datasheet(PDF) 5 Page - Cypress Semiconductor |
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CY14ME064J Datasheet(HTML) 5 Page - Cypress Semiconductor |
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5 / 31 page  CY14MB064J CY14ME064J Document #: 001- 65051 Rev. *B Page 5 of 31 Data Validity The data on the SDA line must be stable during the HIGH period of the clock. The state of the data line can only change when the clock on the SCL line is LOW for the data to be valid. There are only two conditions under which the SDA line may change state with SCL line held HIGH, that is, START and STOP condition. The START and STOP conditions are generated by the master to signal the beginning and end of a communication sequence on the I2C bus. START Condition (S) A HIGH to LOW transition on the SDA line while SCL is HIGH indicates a START condition. Every transaction in I2C begins with the master generating a START condition. STOP Condition (P) A LOW to HIGH transition on the SDA line while SCL is HIGH indicates a STOP condition. This condition indicates the end of the ongoing transaction. START and STOP conditions are always generated by the master. The bus is considered to be busy after the START condition. The bus is considered to be free again after the STOP condition. Repeated START (Sr) If an Repeated START condition is generated instead of a STOP condition the bus continues to be busy. The ongoing transaction on the I2C lines is stopped and the bus waits for the master to send a slave ID for communication to restart. Byte Format Each operation in I2C is done using 8 bit words. The bits are sent in MSB first format on SDA line and each byte is followed by an ACK signal by the receiver. An operation continues till a NACK is sent by the receiver or STOP or Repeated START condition is generated by the master The SDA line must remain stable when the clock (SCL) is HIGH except for a START or STOP condition. Acknowledge / No-acknowledge After transmitting one byte of data or address, the transmitter releases the SDA line. The receiver pulls the SDA line LOW to acknowledge the receipt of the byte. Every byte of data transferred on the I2C bus needs to be responded with an ACK signal by the receiver to continue the operation. Failing to do so is considered as a NACK state. NACK is the state where receiver does not acknowledge the receipt of data and the operation is aborted. NACK can be generated by master during a READ operation in following cases: ■ The master did not receive valid data due to noise ■ The master generates a NACK to abort the READ sequence. After a NACK is issued by the master, nvSRAM slave releases control of the SDA pin and the master is free to generate a Repeated START or STOP condition. NACK can be generated by nvSRAM slave during a WRITE operation in following cases: ■ nvSRAM did not receive valid data due to noise. ■ The master tries to access write protected locations on the nvSRAM. Master must restart the communication by generating a STOP or Repeated START condition. Figure 4. START and STOP Conditions Figure 5. Data Transfer on the I2C Bus full pagewidth SDA SCL P STOP Condition SDA SCL S START Condition handbook, full pagewidth Sr or P SDA Sr P SCL STOP or Repeated START condition S or Sr START or Repeated START condition 1 2 3 - 8 9 ACK 9 ACK 78 12 MSB Acknowledgement signal from slave Byte complete, interrupt within slave Clock line held LOW while interrupts are serviced Acknowledgement signal from receiver [+] Feedback |
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