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IIS328DQ Datasheet(PDF) 18 Page - STMicroelectronics |
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IIS328DQ Datasheet(HTML) 18 Page - STMicroelectronics |
18 / 40 page Digital interfaces IIS328DQ 18/40 DocID027250 Rev 3 5.1.1 I²C operation The transaction on the bus is started through a START (ST) signal. A START condition is defined as a HIGH-to-LOW transition on the data line while the SCL line is held HIGH. After this has been transmitted by the master, the bus is considered busy. The next byte of data transmitted after the start condition contains the address of the slave in the first 7 bits and the eighth bit tells whether the master is receiving data from the slave or transmitting data to the slave. When an address is sent, each device in the system compares the first seven bits after a start condition with its address. If they match, the device considers itself addressed by the master. The slave address (SAD) associated to the IIS328DQ is 001100xb. The SDO/SA0 pad can be used to modify the less significant bit of the device address. If the SA0 pad is connected to voltage supply, LSb is ‘1’ (address 0011001b), otherwise if the SA0 pad is connected to ground, the LSb value is ‘0’ (address 0011000b). This solution permits the connection and addressing of two different accelerometers to the same I²C lines. Data transfer with acknowledge is mandatory. The transmitter must release the SDA line during the acknowledge pulse. The receiver must then pull the data line LOW so that it remains stable low during the HIGH period of the acknowledge clock pulse. A receiver which has been addressed is obliged to generate an acknowledge after each byte of data received. The I²C embedded in the IIS328DQ behaves like a slave device, and the following protocol must be adhered to. After the start condition (ST) a slave address is sent. Once a slave acknowledge (SAK) has been returned, an 8-bit sub-address (SUB) is transmitted: the 7 LSb represent the actual register address while the MSb enables address auto-increment. If the MSb of the SUB field is ‘1’, the SUB (register address) is automatically increased to allow multiple data read/write. The slave address is completed with a read/write bit. If the bit is ‘1’ (read), a repeated START (SR) condition must be issued after the two sub-address bytes; if the bit is ‘0’ (write) the master transmits to the slave with direction unchanged. Table 10 explains how the SAD+Read/Write bit pattern is composed, listing all the possible configurations. Table 10. SAD+Read/Write patterns Command SAD[6:1] SAD[0] = SA0 R/W SAD+R/W Read 001100 0 1 00110001 (31h) Write 001100 0 0 00110000 (30h) Read 001100 1 1 00110011 (33h) Write 001100 1 0 00110010 (32h) Table 11. Transfer when master is writing one byte to slave Master ST SAD + W SUB DATA SP Slave SAK SAK SAK Table 12. Transfer when master is writing multiple bytes to slave Master ST SAD + W SUB DATA DATA SP Slave SAK SAK SAK SAK |
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