PhoenixBios Post Tasks and Beep Codes

When you turn on the 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 I/O port 80h. Programmers and technicians use this code during troubleshooting to establish at what point the system failed and what routine was being performed. Some mainboards are equipped with a seven-segment LED display that displays the current vaule 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), attemps to display the error code on upper left conrner of the screen and on the port 80h LED display, and halts POST. It attempts repeatedly to write the error to the screen.

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.

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