Acer AC100 Acer AC100 Service Guide - Page 101

Chapter 8 BIOS POST codes and messages BIOS POST Messages During the Power-On Self-Test (POST), the BIOS will check for problems. If a problem is found, the BIOS will activate an alarm or display a message. The following is a list of such BIOS messages. POST Code Checkpoints 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, generates a checkpoint code at port 80h or even halts the system if the error is fatal. The main components on the system board that must be diagnosed and/or initialized by POST to ensure system functionality are as follows: • Microprocessor with built-in numeric coprocessor and cache memory subsystem • Direct memory access (DMA) controller (8237 module) • Interrupt system (8259 module) • Three programmable timers (system timer and 8254 module) • ROM subsystem • RAM subsystem • CMOS RAM subsystem and real time clock/calendar with battery backup When POST executes a task, it uses a series of preset numbers called checkpoints to be latched at port 80h, indicating the stages it is currently running. This latch can be read and shown on an external monitor connected to the debug card. Viewing BIOS checkpoints Viewing all checkpoints generated by the BIOS requires a debug card and an external monitor. Checkpoints may appear on the bottom right corner of the screen during POST. Chapter 8 95