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Power-On Self-Test (POST)

Each time you turn on the system, the Power-on Self Test (POST) is initiated. Several items are tested

during POST, but is for the most part transparent to the user.

The Power-On Self Test (POST) is a BIOS procedure that boots the system, initializes and diagnoses the

system components, and controls the operation of the power-on password option. If POST discovers errors

in system operations at power-on, it displays error messages on screen, generates a check point code at

Port 80h or even halts the system if the error is fatal.

The main components on the main board that must be diagnosed and/or initialized by POST to ensure

system functionality are as follows:

z Microprocessor with built-in numeric co-processor and cache memory subsystem

z Direct Memory Access (DMA) controller

z Interrupt system

z Three programmable timer

z ROM subsystem

z RAM subsystem

z CMOS RAM subsystem and real time clock/calendar with battery backup

z Onboard parallel interface controller

z Embedded hard disk interface and one diskette drive interface

z Keyboard and auxiliary device controllers

z I/O ports

z One parallel port

z One PS/2-compatible mouse port

z One PS/2-compatible keyboard port

NOTE: When Post executes a task, it uses a series of preset numbers called check points to be latched

at port 80h, indicating the stages it is currently running. This latch can be read and shown on a

debug board.

The following table describes the BIOS common tasks carried out by POST. Each task is denoted by

an unique check point number. For other unique check point numbers that are not listed in the table,

refer to the corresponding product service guide.

Post Checkpoints List: The list may vary accordingly depending on your BIOS

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Acer EL1800 Technical Information Seite 52