Datasheet ADT7470 (Analog Devices) - 8

ADT7470 Data Sheet GENERAL-PURPOSE I/O PINS (OPEN DRAIN)
The ADT7470 has four pins that can be configured as either general-purpose logic pins or as PWM outputs. Each GPIO pin has a corresponding enable, direction, polarity and status bit.
Pin Function Register Address and Bit
GPIO1 Enable 0x7F [3] Direction 0x80 [7] Polarity 0x80 [6] Status 0x81 [4] GPIO2 Enable 0x7F [2] Direction 0x80 [5] Polarity 0x80 [4] Status 0x81 [5] GPIO3 Enable 0x7F [1] Direction 0x80 [3] Polarity 0x80 [2] Status 0x81 [6] GPIO4 Enable 0x7F [0] Direction 0x80 [1] Polarity 0x80 [0] Status 0x81 [7] To enable the PWM output on the ADT7470 as GPIOs, the enable bits in Register 0x7F must be set to 1. Setting a direction bit to 1 in the GPIO configuration register makes the corresponding GPIO pin an output. Clearing the direction bit to 0 makes it an input. Setting a polarity bit to 1 makes the corresponding GPIO pin active high. Clearing the polarity bit to 0 makes it active low. When a GPIO pin is configured as an input, the corresponding bit in the GPIO status register is read-only and is set when the input is asserted. When a GPIO pin is configured as an output, the corresponding bit in one of the GPIO status registers becomes read/write. Setting this bit asserts the GPIO output. Note that whether a GPIO pin is configured as an input or as an output, asserted can be high or low, depending on the setting of the polarity bit. Rev. E | Page 8 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