The LM78 Microprocessor System Hardware Monitor is a highly integrated Data Acquisition system for hardware monitoring of servers, Personal Computers, or virtually any microprocessor based system. In a PC, the LM78 can be used to monitor power supply voltages, temperatures, and fan speeds. Actual values for these inputs can be read at any time, and programmable WATCHDOG limits in the LM78 activate a fully programmable and maskable interrupt system with two outputs. The LM78 has an on-chip temperature sensor, 5 positive analog inputs, two inverting inputs (for monitoring negative voltages), and an 8-bit ADC. An input is provided for the overtemperature outputs of additional temperature sensors and this is linked to the interrupt system. The LM78 provides inputs for three fan tachometer outputs. Additional inputs are provided for Chassis Intrusion detection circuits, VID monitor inputs, and chainable interrupt. The LM78 provides both ISA and Serial Bus interfaces. A 32-byte auto-increment RAM is provided for POST (Power On Self Test) code storage.
The LM78 is a highly integrated data‑acquisition system for monitoring power‑supply voltages, temperatures, and fan speeds in servers, PCs and other microprocessor‑based systems. It provides on‑chip temperature sensing, five positive analog inputs, two inverting inputs for negative voltages, and an 8‑bit ADC, plus watchdog and interrupt capabilities.
The document includes a full pin description, absolute maximum ratings, DC and AC electrical characteristics, physical dimensions, and a life‑support policy. Typical application circuits and wiring diagrams illustrate how the LM78 can be used to monitor multiple voltages, fan speeds, chassis intrusion, and external temperature sensors via ISA and Serial Bus interfaces.
| Supply Voltage | 5 V |
|---|---|
| Operating Supply Current | 1 mA typ |
| ADC Resolution | 8 bits |
| Temperature Accuracy | +3 °C (max) over –10 °C to +100 °C |
| Number of Positive Analog Inputs | 5 |
| Number of Inverting Inputs | 2 |
| Fan Speed Monitoring Inputs | 3 |
The LM78 operates from a 5 V supply.
The device provides five positive analog inputs and two inverting inputs for negative voltages.
The analog‑to‑digital converter has an 8‑bit resolution.
Yes, programmable watchdog limits generate a maskable interrupt with two outputs.