NEC MH4500 manual Messages and Beep Codes, Post Tests, Code Beeps Post Routine Description

Messages and Beep Codes

Whenever a recoverable error occurs during POST, BIOS displays a message on the video display screen and causes the speaker to beep twice as the message appears. BIOS also issues a beep code (one long tone followed by two short tones) during POST if the video configuration fails or if an external ROM module does not checksum to zero.

At the beginning of each POST test routine, the BIOS outputs the test point error code to I/O address 80h. If the BIOS detects a terminal error condition, it halts POST after issuing a terminal error beep code signifying the test point code and attempting to display the test point error code on the upper left corner of the display screen. BIOS derives the beep code from the test point error code.

For example, a test point error code of 16 is indicated by a 1-2-2-3 beep code (a single beep, a burst of two beeps, a burst of two beeps, and a burst of three beeps). In addition, BIOS writes a value of 16 on the upper left corner of the display screen and to I/O port 80h to enable debugging tools to identify the area of failure.

The following table is a list of the test point error codes written at the start of each POST test and the beep codes issued for terminal errors.

POST Tests

Code Beeps POST Routine Description

xx1-1-1-1 There are no processors present in the system, or the processors are so incompatible that the system BIOS cannot be run (like mismatched cache voltages).

02	Verify Real Mode
04	Get CPU type
06	Initialize system hardware
08	Initialize chipset registers with initial POST values
09	Set in POST flag
0A	Initialize CPU registers
0C	Initialize cache to initial POST values
0E	Initialize I/O
0F	Initialize the local bus IDE
10	Initialize Power Management
11	Load alternate registers with initial POST values
12	Restore CPU control word during warm boot
14	Initialize keyboard controller
16	1-2-2-3 BIOS ROM checksum
18	8254 timer initialization
1A	8237 DMA controller initialization

Solving Problems 5-17