Datasheet ADT7470 (Analog Devices) - 33

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Data Sheet ADT7470 Table 36. Register 0x58 to Register 0x67. Fan Tachometer Limit Registers. Register Address Read/Write Description Power-On Default
0x58 Read/Write Tach 1 min low byte 0xFF 0x59 Read/Write Tach 1 min high byte 0xFF 0x5A Read/Write Tach 2 min low byte 0xFF 0x5B Read/Write Tach 2 min high byte 0xFF 0x5C Read/Write Tach 3 min low byte 0xFF 0x5D Read/Write Tach 3 min high byte 0xFF 0x5E Read/Write Tach 4 min low byte 0xFF 0x5F Read/Write Tach 4 min high byte 0xFF 0x60 Read/Write Tach 1 max low byte 0x00 0x61 Read/Write Tach 1 max high byte 0x00 0x62 Read/Write Tach 2 max low byte 0x00 0x63 Read/Write Tach 2 max high byte 0x00 0x64 Read/Write Tach 3 max low byte 0x00 0x65 Read/Write Tach 3 max high byte 0x00 0x66 Read/Write Tach 4 max low byte 0x00 0x67 Read/Write Tach 4 max high byte 0x00 Exceeding any of the tach min limit registers shown in Table 36 by 1 indicates that the fan is running too slowly or has stalled. The appropriate status bit is set in Interrupt Status Register 2 to indicate the fan failure. Exceeding any of the tach max limit registers by 1 indicates that the fan is too fast. The appropriate status bit is set in Interrupt Status Register 2 to indicate the fan failure.
Table 37. Register 0x68. PWM1/PWM2 Configuration Register (Power-On Default = 0x00). Bit Name Read/Write Description
[0] N/A Set to 0 (default). [1] N/A Set to 0 (default). [2] N/A Set to 0 (default). [3] N/A Set to 0 (default). [4] INV2 Read/Write Setting this bit to 1 inverts the PWM2 output. Default = 0. [5] INV1 Read/Write Setting this bit to 1 inverts the PWM1 output. Default = 0. [6] BHVR2 Read/Write This bit assigns fan behavior for PWM2 output. 0 = manual fan control mode (PWM duty cycle controlled in software). 1 = automatic fan control mode [7] BHVR1 Read/Write This bit assigns fan behavior for PWM1 output. 0 = manual fan control mode (PWM duty cycle controlled in software). 1 = automatic fan control mode. Rev. E | Page 33 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