38 BCS Priliminary Model Test.pdf

Lesson 5 : Using Post and After Boot Diagnostics Software 

5.1. Learning Objectives
On completion of this lesson you will be able to describe:
 Power on self test
 Some diagnostics software package.

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5.2. Introduction 

Diagnostic programs are used to detect PC problems. Different types of diagnostics programs are: 

 The power on self test (POST) 

 After boot diagnostics software 

 ROM based diagnostics tools. Some components of the PC should run to run the diagnostics software. These are: 

 The motherboard (including CPU and RAM). Because if they do not run, no other devices will run  The monitor and the video card should run interact with the user. 

 The keyboard should run to get user input 

 The floppy drive should run to load the program. 

5.3. The Power on Self Test (POST) 

Every time the PC is powered-on this program is run. It checks if the basic hardware (CPU, RAM etc.) exists and tests the memory. The checking done by IBM PC-1 BIOS is discussed here. Checking done by other BIOS is nearly similar. POST in IBM PC-1 BIOS checks the following things sequentially: 

 CPU registers and flags. If faulty then halts. 

 ROM checksum. If faulty then halts. 

 DMA controller. If faulty then halts. 

 Interrupt controller. If faulty then POST makes a long beep and a short beep and then halts. 

 Timer and its speed. If faulty then POST makes a long beep and a short beep and then halts. 

 BASIC ROM. If faulty then makes a long beep and a short beep and then halts.

 Video controller. If faulty then it makes a long beep and a short beep and then halts. 

 Installed adapters. If okay then let them (the adapters) initialize. 

 CRT Interface lines. If okay then blinks the cursor. 

 All system RAM. 

 Keyboard. If faulty then makes a short beep but does not halt. 

 Cassette interface. If faulty then makes a short beep but does not halt. 

 Diskette adapter and drive ‘A:’. If faulty then makes a short beep but does not halt. 

 Determines how many printers, serial ports and game ports are connected. Then makes a short beep and starts booting.