Datasheet ADT7470 (Analog Devices) - 10

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ADT7470 Data Sheet
during the low period before the 10th clock pulse, then To write data to one of the device data registers or read data high during the 10th clock pulse to assert a stop condition. from it, the address pointer register must be set so that the Any number of bytes of data can be transferred over the serial correct data register is addressed. Then data can be written into bus in one operation. However, it is not possible to mix read that register or read from it. The first byte of a write operation and write in one operation, because the type of operation is always contains an address that is stored in the address pointer determined at the beginning and subsequently cannot be register. If data is to be written to the device, the write operation changed without starting a new operation. contains a second data byte that is written to the register selected by the address pointer register. In the ADT7470, write operations contain either one or two bytes, and read operations contain one byte and perform the This is illustrated in Figure 7. The device address is sent over the following functions. bus followed by R/W set to 0. This is followed by two data bytes.
1 9 1 9 SCL SDA 0 1 0 1 1 A1 A0 R/W D7 D6 D5 D4 D3 D2 D1 D0 START BY ACK. BY ACK. BY MASTER ADT7470 ADT7470 FRAME 1 FRAME 2 SERIAL BUS ADDRESS ADDRESS POINTER REGISTER BYTE BYTE 1 9 SCL (CONTINUED) SDA (CONTINUED) D7 D6 D5 D4 D3 D2 D1 D0 ACK. BY STOP BY ADT7470 MASTER FRAME 3 DATA BYTE
04684-0-007 Figure 7. Writing a Register Address to the Address Pointer Register, Then Writing Data to the Selected Register
1 9 1 9 SCL SDA 0 1 0 1 1 A1 A0 R/W D7 D6 D5 D4 D3 D2 D1 D0 START BY ACK. BY ACK. BY STOP BY MASTER ADT7470 ADT7470 MASTER FRAME 1 FRAME 2 SERIAL BUS ADDRESS ADDRESS POINTER REGISTER BYTE BYTE
04684-0-008 Figure 8. Writing to the Address Pointer Register Only
1 9 1 9 SCL SDA 0 1 0 1 1 A1 A0 R/W D7 D6 D5 D4 D3 D2 D1 D0 START BY ACK. BY NO ACK. STOP BY MASTER ADT7470 BY MASTER MASTER FRAME 1 FRAME 2 SERIAL BUS ADDRESS DATA BYTE FROM BYTE ADT7470
04684-0-009 Figure 9. Reading Data from a Previously Selected Register Rev. E | Page 10 of 40 Document Outline Features Applications General Description Functional Block Diagram Revision History Specifications Serial Bus Timing Specifications Absolute Maximum Ratings Thermal Characteristics ESD Caution Pin Configuration and Function Descriptions Functional Description General Description ADT7470 Monitoring Cycle Configuration Register 1 (Address 0x40) Configuration Register 2 (Address 0x74) ID Registers General-Purpose I/O Pins (Open Drain) SMBus/I2C Serial Interface Address Selection Serial Bus Protocol Write Operations Send Byte Write Byte Read Operations Receive Byte Alert Response Address SMBus Timeout Temperature Measurement Using TMP05/TMP06 Measuring Temperature TMP05/TMP06 Decoder Temperature ReadBack By the Host Temperature Data Format Temperature Measurement Limits Thermal Zones for Automatic Fan Control Thermal Zone TMIN Limit and Status Registers Limit Values Temperature Limits Fan Speed Limits Out-of-Limit Comparisons Status Registers SMBALERT Interrupt Handling SMBALERT Interrupts Masking Interrupt Sources Enabling the SMBALERT Interrupt Output Fan Drive Using PWM Control High Frequency Fan Drive Low Frequency Fan Drive Setting the Fan Drive Frequency Inverted PWM Output Fan Full Speed Function Fan Speed Measurement Tach Inputs Pulse Stretching Disabling Tach measurement Fan Speed Measurement Fan Speed Measurement Registers Reading Fan Speed from the ADT7470 Fan Tach Limit Registers Fan Speed Measurement Rate Calculating Fan Speed and Tachometer Limits Fan Pulses per Revolution Manual Fan Speed Control Setting the PWM Duty Cycle Example 1: For a PWM Duty Cycle of 50% Example 2: For a PWM Duty Cycle of 33% Automatic Fan Speed Control PWM Min Duty Cycle Example: For a PWM Min Duty Cycle of 30% PWN Max Duty Cycle PWM Current Duty Cycle Register Map Detailed Register Descriptions Outline Dimensions Ordering Guide