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ADT7475 数据表(PDF) 10 Page - ON Semiconductor |
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ADT7475 数据表(HTML) 10 Page - ON Semiconductor |
10 / 58 page ADT7475 http://onsemi.com 10 It is possible to read a data byte from a data register without first writing to the address pointer register if the address pointer register is already at the correct value. However, it is not possible to write data to a register without writing to the address pointer register because the first data byte of a write is always written to the address pointer register. In addition to supporting the send byte and receive byte protocols, the ADT7475 also supports the read byte protocol (for more information, see System Management Bus Specifications Rev. 2.0, available from Intel). If several read or write operations must be performed in succession, the master can send a repeat start condition instead of a stop condition to begin a new operation. Write Operations The SMBus specification defines several protocols for different types of read and write operations. The ones used in the ADT7475 are discussed in this section. The following abbreviations are used in the diagrams: S − Start P − Stop R − Read W − Write A − Acknowledge A − No acknowledge The ADT7475 uses the following SMBus write protocols. Send Byte In this operation, the master device sends a single command byte to a slave device as follows: 1. The master device asserts a start condition on SDA. 2. The master sends the 7-bit slave address followed by the write bit (low). 3. The addressed slave device asserts ACK on SDA. 4. The master sends a command code. 5. The slave asserts ACK on SDA. 6. The master asserts a stop condition on SDA and the transaction ends. For the ADT7475, the send byte protocol is used to write a register address to RAM for a subsequent single-byte read from the same address. This operation is shown in Figure 16. Figure 16. Setting a Register Address for Subsequent Read SLAVE ADDRESS WA SA P REGISTER ADDRESS 23 15 6 4 If the master is required to read data from the register immediately after setting up the address, it can assert a repeat start condition immediately after the final ACK and carry out a single-byte read without asserting an intermediate stop condition. Write Byte In this operation, the master device sends a command byte and one data byte to the slave device as follows: 1. The master device asserts a start condition on SDA. 2. The master sends the 7-bit slave address followed by the write bit (low). 3. The addressed slave device asserts ACK on SDA. 4. The master sends a command code. 5. The slave asserts ACK on SDA. 6. The master sends a data byte. 7. The slave asserts ACK on SDA. 8. The master asserts a stop condition on SDA and the transaction ends. The byte write operation is shown in Figure 17. Figure 17. Single-byte Write to a Register SLAVE ADDRESS W A DATA SA A P REGISTER ADDRESS 23 15 6 7 8 4 Read Operations The ADT7475 uses the following SMBus read protocols. Receive Byte This operation is useful when repeatedly reading a single register. The register address must be set up previously. In this operation, the master device receives a single byte from a slave device as follows: 1. The master device asserts a start condition on SDA. 2. The master sends the 7-bit slave address followed by the read bit (high). 3. The addressed slave device asserts ACK on SDA. 4. The master receives a data byte. 5. The master asserts NO ACK on SDA. 6. The master asserts a stop condition on SDA, and the transaction ends. In the ADT7475, the receive byte protocol is used to read a single byte of data from a register whose address has previously been set by a send byte or write byte operation. This operation is shown in Figure 18. Figure 18. Single-byte Read from a Register SLAVE ADDRESS DATA A R SA P 24 3 15 6 Alert Response Address Alert response address (ARA) is a feature of SMBus devices that allows an interrupting device to identify itself to the host when multiple devices exist on the same bus. The SMBALERT output can be used as either an interrupt output or an SMBALERT. One or more outputs can be connected to a common SMBALERT line connected to the |
类似零件编号 - ADT7475_13 |
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类似说明 - ADT7475_13 |
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