POST Tasks and Beep Codes
When you turn on or reset an IBM- compatible PC, the BIOS first performs a number of tasks, called the Power- On- Self- Test (POST). These tasks test and initialize the hardware and then boot the Operating System from the hard disk.
At the beginning of each POST task, the BIOS outputs the test- point error code to I/ O port 80h. Programmers and technicians use this code during trouble shooting to establish at what point the system failed and what routine was being performed. Some motherboards are equipped with a seven- segment LED display that displays the current value of port 80h. For production boards which do not contain the LED display, you can purchase an installable "Port 80h" card that performs the same function. If the BIOS detects a terminal error condition, it issues a terminal- error beep code (See following), attempts to display the error code on upper left corner of the screen and on the port 80h LED display, and halts POST. It attempts repeatedly to write the error to the screen. This attempt may "hash" some CGA displays. If the system hangs before the BIOS can process the error, the value displayed at the port 80h is the last test performed. In this case, the screen does not display the error code.
Terminal POST Errors
There are several POST routines that require success to finish POST. If they fail, they issue a POST Terminal Error and shut down the system. Before shutting down the system, the error handler issues a beep code signifying the test point error, writes the error to port 80h, attempts to initialize the video, and writes the error in the upper left corner of the screen (using both mono and color adapters).
Search: Cosmos | BlogPulse
Submit: Digg This | Shout this! | Slashdot
Bookmark: Del.icio.us | Furl It | Spurl | Tag!RawSugar | Simpy This! | Shadows Tag! | Blink It | My Web
GirlGeekteete dotNet Tags: bios, beep codes, phoenix, post, error, ibm, pc, compatible, cga, led, rom, award, nmi, restore, cache, rom
Technorati Tags: bios, beep, codes, phoenix, post, error, ibm, pc, compatible, cga, led, rom, award, nmi, restore, cache, rom
No Comments »
