LM78 Microprocessor System Hardware Monitor
February 2000
LM78
Microprocessor System Hardware Monitor
General Description
The LM78 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, tem-
peratures, 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.
Features
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Temperature sensing
5 positive voltage inputs
2 op amps for negative voltage monitoring
3 fan speed monitoring inputs
Input for additional temperature sensors
Chassis Intrusion Detector input
WATCHDOG comparison of all monitored values
POST code storage RAM
ISA and I
2
C
™
Serial Bus interfaces
Key Specifications
j
Voltage monitoring
accuracy
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Temperature Accuracy
±
1% (max)
±
3˚C (max)
5V
Operating:
Shutdown:
1 mA typ
10 µA typ
8 Bits
−10˚C to +100˚C
j
Supply Voltage
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Supply Current
j
ADC Resolution
Applications
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System Hardware Monitoring for Servers and PCs
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Office Electronics
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Electronic Test Equipment and Instrumentation
Typical Application
DS012873-1
#
indicates Active Low (”Not“)
I2C
®
is a registered trademark of the Phillips Corporation.
© 2001 National Semiconductor Corporation
DS012873
www.national.com
NSC [ NATIONAL SEMICONDUCTOR ]
