Datasheet MAX31889 (Maxim) - 10

link to page 10 MAX31889 ±0.25°C Accurate I2C Temperature Sensor
Alarm Signaling
After the device performs a temperature conversion, the temperature value is compared with the user-defined two’s complement alarm trigger values stored in the 2-byte Alarm High and 2-byte Alarm Low registers (see Figure 2). The default value for AH is 0x7FFF (+163.835°C) and the default value for AL is 0x8000 (-163.840°C). The MSB indicates if the value is positive or negative; for positive numbers the MSB is 0 and for negative numbers the MSB is 1. The Alarm High threshold (AH) is programmed in registers ALARM_HI_MSB [0x10] and ALARM_HI_LSB [0x11]. The alarm low threshold (AL) is programmed in registers ALARM_LO_MSB [0x12] and ALARM_LO_LSB [0x13]. If the measured temperature is lower than AL or higher than AH, an alarm condition exists and corresponding status bit, TEMP_LO or TEMP_HI is set in the STATUS [0x00] regsiter. When the alarm condition is detected and the corresponding interrupt enable bit, TEMP_LO_EN or TEMP_HI_EN is set in the INTERRUPT_ENABLE [0x01] register and if GPIO0_MODE in the GPIO_SETUP [0x20] register is set to 0x3 then a hardware interrupt asserts on the GPIO0 pin. The status bits, the alarm flag and the hardware interrupt stay asserted until the STATUS [0x00] register is read through the serial interface. The alarm flag only clears when STATUS is read. If the alarm flag is set and the next result does not trip the flag, then the flag remains set. If the resolution or alarm settings change while the device is under an alarm condition, the alarm status must be cleared and another temperature conversion executed to update the alarm condition. ALARM HIGH THRESHOLD REGISTER FORMAT Bit15 Bit14 Bit13 Bit12 Bit11 Bit10 Bit9 Bit8 MSB AH15 AH14 AH13 AH12 AH11 AH10 AH9 AH8 Bit7 Bit6 Bit5 Bit4 Bit3 Bit2 Bit1 Bit0 LSB AH7 AH6 AH5 AH4 AH3 AH2 AH1 AH0 ALARM LOW THRESHOLD REGISTER FORMAT Bit15 Bit14 Bit13 Bit12 Bit11 Bit10 Bit9 Bit8 MSB AL15 AL14 AL13 AL12 AL11 AL10 AL9 AL8 Bit7 Bit6 Bit5 Bit4 Bit3 Bit2 Bit1 Bit0 LSB AL7 AL6 AL5 AL4 AL3 AL2 AL1 AL0 Figure 2. Alarm Threshold Register Format 19-100693 www.maximintegrated.com Maxim Integrated | 10 Document Outline General Description Applications Benefits and Features Simplified Block Diagram Absolute Maximum Ratings Package Information μDFN Electrical Characteristics Electrical Characteristics (continued) Typical Operating Characteristics Typical Operating Characteristics (continued) Pin Configuration μDFN Pin Description Functional Diagrams Detailed Description Operation Measuring Temperature Alarm Signaling GPIO I2C I2C Slave Address I2C/SMBus Compatible Serial Interface Detailed I2C Timing Diagram Bit Transfer START and STOP Conditions Early STOP Conditions Acknowledge Bit I2C Write Data Format I2C Read Data Format FIFO Description Register Map Register Map Register Details STATUS (0x0) INTERRUPT ENABLE (0x1) FIFO WRITE POINTER (0x04) FIFO READ POINTER (0x05) FIFO OVERFLOW COUNTER (0x06) FIFO DATA COUNTER (0x07) FIFO DATA (0x08) FIFO CONFIGURATION 1 (0x09) FIFO CONFIGURATION 2 (0x0A) SYSTEM CONTROL (0x0C) ALARM HIGH MSB (0x10) ALARM HIGH LSB (0x11) ALARM LOW MSB (0x12) ALARM LOW LSB (0x13) TEMP SENSOR SETUP (0x14) GPIO SETUP (0x20) GPIO CONTROL (0x21) ROM ID 1 (0x31) ROM ID 2 (0x32) ROM ID 3 (0x33) ROM ID 4 (0x34) ROM ID 5 (0x35) ROM ID 6 (0x36) PART IDENTIFIER (0xFF) Applications Information Measurement Considerations Typical Application Circuit Ordering Information Revision History