## Overview of the LM87CIMT The **LM87CIMT** is a highly integrated data acquisition system designed primarily for hardware monitoring in servers, workstations, and high-performance PCs. It is manufactured by Texas Instruments (formerly National Semiconductor). ### Key Functions The device acts as a "watchdog" for a system's physical health, monitoring three critical areas: 1. **Voltages:** Monitors multiple power rails. 2. **Temperature:** Measures internal die temperature and external diode temperatures. 3. **Fan Speed:** Tracks RPMs of cooling fans. --- ### Technical Specifications | Parameter | Specification | | :--- | :--- | | **Supply Voltage (Vcc)** | 2.8V to 3.8V | | **Interface** | I2C / SMBus Serial Interface | | **ADC Resolution** | 8-Bit | | **Voltage Inputs** | 7 Positive Voltage Inputs | | **Temperature Inputs** | 1 Internal, 2 Remote Diode Inputs | | **Package Type** | TSSOP-24 | | **Operating Temp Range** | -40°C to +125°C | --- ### Internal Electronic Architecture The LM87CIMT consists of several internal modules that work together to provide digitized health data to the host processor: #### 1. Analog-to-Digital Converter (ADC) The heart of the chip is an 8-bit successive approximation ADC. It multiplexes between the voltage and temperature inputs, converting analog signals into digital values that can be read over the I2C bus. #### 2. Temperature Sensors * **Internal:** Uses an on-chip bandgap sensor. * **Remote:** Uses "Diode Input" pins to measure the temperature of external transistors (like those found inside a CPU or GPU) by measuring the differential voltage across a P-N junction. #### 3. Fan Speed Monitoring The chip features inputs for **Fan Tachometer** signals. It counts pulses from the fan's tach output against an internal clock to determine the rotation speed. #### 4. Interrupt Logic (INT) The LM87 contains programmable registers for "High" and "Low" limits. If a voltage or temperature exceeds these bounds, the chip triggers an interrupt signal on the **INT** pin to alert the system controller immediately. --- ### Typical Pin Configuration (Selection) | Pin Name | Function | | :--- | :--- | | **SDA / SCL** | Serial Data and Clock for I2C communication. | | **D+ / D-** | Connections for external temperature-sensing diodes. | | **FAN1 / FAN2** | Inputs for fan tachometer signals. | | **AIN1 - AIN7** | Analog inputs for monitoring various voltage rails (e.g., 2.5V, 3.3V, 5V, 12V). | | **Vcc / GND** | Power supply and ground pins. |