Code Description of POST Operation
D0 NMI is Disabled. Onboard KBC, RTC enabled (if present). Init code Checksum verification starting.
D1 Keyboard controller BAT test, CPU ID saved, and going to 4 GB flat mode.
D3 Do necessary chipset initialization, start memory refresh, and do memory sizing.
D4 Verify base memory.
D5 Init code to be copied to segment 0 and control to be transferred to segment 0.
D6 Control is in segment 0. To check recovery mode and verify main BIOS checksum. If either it is
recovery mode or main BIOS checksum is bad, go to check point E0 for recovery else go to check
point D7 for giving control to main BIOS.
D7 Find Main BIOS module in ROM image.
D8 Uncompress the main BIOS module.
D9 Copy main BIOS image to F000 shadow RAM and give control to main BIOS in F000 shadow RAM.
E0 Onboard Floppy Controller (if any) is initialized. Compressed recovery code is uncompressed in
F000:0000 in Shadow RAM and give control to recovery code in F000 Shadow RAM. Initialize
interrupt vector tables, initialize system timer, initialize DMA controller and interrupt controller.
E8 Initialize extra (Intel Recovery) Module.
E9 Initialize floppy drive.
EA Try to boot from floppy. If reading of boot sector is successful, give control to boot sector code.
EB Booting from floppy failed, look for ATAPI (LS-120, Zip) devices.
EC Try to boot from ATAPI. If reading of boot sector is successful, give control to boot sector code.
EF Booting from floppy and ATAPI device failed. Give two beeps. Retry the booting procedure again
(go to check point E9).
03 NMI is Disabled. To check soft reset/power-on.
05 BIOS stack set. Going to disable cache if any.
06 POST code to be uncompressed.
07 CPU init and CPU data area init to be done.
08 CMOS checksum calculation to be done next.
0B Any initialization before keyboard BAT to be done next.
0C KB controller I/B free. To issue the BAT command to keyboard controller.
0E Any initialization after KB controller BAT to be done next.
0F Keyboard command byte to be written.
10 Going to issue Pin-23,24 blocking/unblocking command.
11 Going to check pressing of <INS>, <END> key during power-on.
12 To init CMOS if "Init CMOS in every boot" is set or <END> key is pressed. Going to disable DMA
and Interrupt controllers.
13 Video display is disabled and port-B is initialized. Chipset init about to begin.
14 8254 timer test about to start.
19 About to start memory refresh test.
1A Memory Refresh line is toggling. Going to check 15 µs ON/OFF time.
23 To read 8042 input port and disable Megakey GreenPC feature. Make BIOS code segment
writeable.
24 To do any setup before Int vector init.
25 Interrupt vector initialization to begin. To clear password if necessary.
27 Any initialization before setting video mode to be done.
28 Going for monochrome mode and color mode setting.
2A Different buses init (system, static, output devices) to start if present. (See Section 4.3 for details
of different buses.)
2B To give control for any setup required before optional video ROM check.
2C To look for optional video ROM and give control.
2D To give control to do any processing after video ROM returns control.
2E If EGA/VGA not found then do display memory R/W test.
2F EGA/VGA not found. Display memory R/W test about to begin.
30 Display memory R/W test passed. About to look for the retrace checking.
31 Display memory R/W test or retrace checking failed. To do alternate Display memory R/W test.
32 Alternate Display memory R/W test passed. To look for the alternate display retrace checking.
34 Video display checking over. Display mode to be set next.
37 Display mode set. Going to display the power-on message.
38 Different buses init (input, IPL, general devices) to start if present. (See Section 4.3 for details of
different buses.)
39 Display different buses initialization error messages. (See Section 4.3 for details of different
buses.)
3A New cursor position read and saved. To display the Hit <DEL> message.
40 To prepare the descriptor tables.
42 To enter in virtual mode for memory test.
43 To enable interrupts for diagnostics mode.
44 To initialize data to check memory wrap around at 0:0.
45 Data initialized. Going to check for memory wrap around at 0:0 and finding the total system
memory size.
46 Memory wrap around test done. Memory size calculation over. About to go for writing patterns to
test memory.
47 Pattern to be tested written in extended memory. Going to write patterns in base 640k memory.
48 Patterns written in base memory. Going to find out amount of memory below 1M memory.
49 Amount of memory below 1M found and verified. Going to find out amount of memory above 1M
memory.
4B Amount of memory above 1M found and verified. Check for soft reset and going to clear memory
below 1M for soft reset. (If power on, go to check point # 4Eh).
4C Memory below 1M cleared. (SOFT RESET) Going to clear memory above 1M.
4D Memory above 1M cleared. (SOFT RESET) Going to save the memory size. (Go to check
point # 52h).
4E Memory test started. (NOT SOFT RESET) About to display the first 64k memory size.
4F Memory size display started. This will be updated during memory test. Going for sequential and
random memory test.
50 Memory testing/initialization below 1M complete. Going to adjust displayed memory size for
relocation/shadow.
51 Memory size display adjusted due to relocation/ shadow. Memory test above 1M to follow.
52 Memory testing/initialization above 1M complete. Going to save memory size information.
53 Memory size information is saved. CPU registers are saved. Going to enter in real mode.
54 Shutdown successful, CPU in real mode. Going to disable gate A20 line and disable parity/NMI.
57 A20 address line, parity/NMI disable successful. Going to adjust memory size depending on
relocation/shadow.
58 Memory size adjusted for relocation/shadow. Going to clear Hit <DEL> message.
59 Hit <DEL> message cleared. <WAIT...> message displayed. About to start DMA and interrupt
controller test.
60 DMA page register test passed. To do DMA#1 base register test.
62 DMA#1 base register test passed. To do DMA#2 base register test.
65 DMA#2 base register test passed. To program DMA unit 1 and 2.
66 DMA unit 1 and 2 programming over. To initialize 8259 interrupt controller.
7F Extended NMI sources enabling is in progress.
80 Keyboard test started. Clearing output buffer, checking for stuck key, to issue keyboard reset
command.
81 Keyboard reset error/stuck key found. To issue keyboard controller interface test command.
82 Keyboard controller interface test over. To write command byte and init circular buffer.
83 Command byte written, global data init done. To check for lock-key.
84 Lock-key checking over. To check for memory size mismatch with CMOS.
85 Memory size check done. To display soft error and check for password or bypass setup.
86 Password checked. About to do programming before setup.
87 Programming before setup complete. To uncompress SETUP code and execute CMOS setup.
88 Returned from CMOS setup program and screen is cleared. About to do programming after setup.
89 Programming after setup complete. Going to display power-on screen message.
8B First screen message displayed. <WAIT...> message displayed. PS/2 Mouse check and
extended BIOS data area allocation to be done.
8C Setup options programming after CMOS setup about to start.
8D Going for hard disk controller reset.
8F Hard disk controller reset done. Floppy setup to be done next.
91 Floppy setup complete. Hard disk setup to be done next.
95 Init of different buses optional ROMs from C800 to start. (See Section 4.3 for details of different
buses.)
96 Going to do any init before C800 optional ROM control.
97 Any init before C800 optional ROM control is over. Optional ROM check and control will be
done next.
98 Optional ROM control is done. About to give control to do any required processing after optional
ROM returns control and enable external cache.
99 Any initialization required after optional ROM test over. Going to setup timer data area and printer
base address.
9A Return after setting timer and printer base address. Going to set the RS-232 base address.
9B Returned after RS-232 base address. Going to do any initialization before Coprocessor test.
9C Required initialization before Coprocessor is over. Going to initialize the Coprocessor next.
9D Coprocessor initialized. Going to do any initialization after Coprocessor test.
9E Initialization after Coprocessor test is complete. Going to check extended keyboard, keyboard ID
and num-lock.
A2 Going to display any soft errors.
A3 Soft error display complete. Going to set keyboard typematic rate.
A4 Keyboard typematic rate set. To program memory wait states.
A5 Going to enable parity/NMI.
A7 NMI and parity enabled. Going to do any initialization required before giving control to optional
ROM at E000.
A8 Initialization before E000 ROM control over. E000 ROM to get control next.
A9 Returned from E000 ROM control. Going to do any initialization required after E000 optional ROM
control.
AA Initialization after E000 optional ROM control is over. Going to display the system configuration.
AB Put INT13 module runtime image to shadow.
AC Generate MP for multiprocessor support (if present).
AD Put CGA INT10 module (if present) in Shadow.
AE Uncompress SMBIOS module and init SMBIOS code and form the runtime SMBIOS image in
shadow.
B1 Going to copy any code to specific area.
00 Copying of code to specific area done. Going to give control to INT-19 boot loader.
D0 NMI is Disabled. Onboard KBC, RTC enabled (if present). Init code Checksum verification starting.
D1 Keyboard controller BAT test, CPU ID saved, and going to 4 GB flat mode.
D3 Do necessary chipset initialization, start memory refresh, and do memory sizing.
D4 Verify base memory.
D5 Init code to be copied to segment 0 and control to be transferred to segment 0.
D6 Control is in segment 0. To check recovery mode and verify main BIOS checksum. If either it is
recovery mode or main BIOS checksum is bad, go to check point E0 for recovery else go to check
point D7 for giving control to main BIOS.
D7 Find Main BIOS module in ROM image.
D8 Uncompress the main BIOS module.
D9 Copy main BIOS image to F000 shadow RAM and give control to main BIOS in F000 shadow RAM.
E0 Onboard Floppy Controller (if any) is initialized. Compressed recovery code is uncompressed in
F000:0000 in Shadow RAM and give control to recovery code in F000 Shadow RAM. Initialize
interrupt vector tables, initialize system timer, initialize DMA controller and interrupt controller.
E8 Initialize extra (Intel Recovery) Module.
E9 Initialize floppy drive.
EA Try to boot from floppy. If reading of boot sector is successful, give control to boot sector code.
EB Booting from floppy failed, look for ATAPI (LS-120, Zip) devices.
EC Try to boot from ATAPI. If reading of boot sector is successful, give control to boot sector code.
EF Booting from floppy and ATAPI device failed. Give two beeps. Retry the booting procedure again
(go to check point E9).
03 NMI is Disabled. To check soft reset/power-on.
05 BIOS stack set. Going to disable cache if any.
06 POST code to be uncompressed.
07 CPU init and CPU data area init to be done.
08 CMOS checksum calculation to be done next.
0B Any initialization before keyboard BAT to be done next.
0C KB controller I/B free. To issue the BAT command to keyboard controller.
0E Any initialization after KB controller BAT to be done next.
0F Keyboard command byte to be written.
10 Going to issue Pin-23,24 blocking/unblocking command.
11 Going to check pressing of <INS>, <END> key during power-on.
12 To init CMOS if "Init CMOS in every boot" is set or <END> key is pressed. Going to disable DMA
and Interrupt controllers.
13 Video display is disabled and port-B is initialized. Chipset init about to begin.
14 8254 timer test about to start.
19 About to start memory refresh test.
1A Memory Refresh line is toggling. Going to check 15 µs ON/OFF time.
23 To read 8042 input port and disable Megakey GreenPC feature. Make BIOS code segment
writeable.
24 To do any setup before Int vector init.
25 Interrupt vector initialization to begin. To clear password if necessary.
27 Any initialization before setting video mode to be done.
28 Going for monochrome mode and color mode setting.
2A Different buses init (system, static, output devices) to start if present. (See Section 4.3 for details
of different buses.)
2B To give control for any setup required before optional video ROM check.
2C To look for optional video ROM and give control.
2D To give control to do any processing after video ROM returns control.
2E If EGA/VGA not found then do display memory R/W test.
2F EGA/VGA not found. Display memory R/W test about to begin.
30 Display memory R/W test passed. About to look for the retrace checking.
31 Display memory R/W test or retrace checking failed. To do alternate Display memory R/W test.
32 Alternate Display memory R/W test passed. To look for the alternate display retrace checking.
34 Video display checking over. Display mode to be set next.
37 Display mode set. Going to display the power-on message.
38 Different buses init (input, IPL, general devices) to start if present. (See Section 4.3 for details of
different buses.)
39 Display different buses initialization error messages. (See Section 4.3 for details of different
buses.)
3A New cursor position read and saved. To display the Hit <DEL> message.
40 To prepare the descriptor tables.
42 To enter in virtual mode for memory test.
43 To enable interrupts for diagnostics mode.
44 To initialize data to check memory wrap around at 0:0.
45 Data initialized. Going to check for memory wrap around at 0:0 and finding the total system
memory size.
46 Memory wrap around test done. Memory size calculation over. About to go for writing patterns to
test memory.
47 Pattern to be tested written in extended memory. Going to write patterns in base 640k memory.
48 Patterns written in base memory. Going to find out amount of memory below 1M memory.
49 Amount of memory below 1M found and verified. Going to find out amount of memory above 1M
memory.
4B Amount of memory above 1M found and verified. Check for soft reset and going to clear memory
below 1M for soft reset. (If power on, go to check point # 4Eh).
4C Memory below 1M cleared. (SOFT RESET) Going to clear memory above 1M.
4D Memory above 1M cleared. (SOFT RESET) Going to save the memory size. (Go to check
point # 52h).
4E Memory test started. (NOT SOFT RESET) About to display the first 64k memory size.
4F Memory size display started. This will be updated during memory test. Going for sequential and
random memory test.
50 Memory testing/initialization below 1M complete. Going to adjust displayed memory size for
relocation/shadow.
51 Memory size display adjusted due to relocation/ shadow. Memory test above 1M to follow.
52 Memory testing/initialization above 1M complete. Going to save memory size information.
53 Memory size information is saved. CPU registers are saved. Going to enter in real mode.
54 Shutdown successful, CPU in real mode. Going to disable gate A20 line and disable parity/NMI.
57 A20 address line, parity/NMI disable successful. Going to adjust memory size depending on
relocation/shadow.
58 Memory size adjusted for relocation/shadow. Going to clear Hit <DEL> message.
59 Hit <DEL> message cleared. <WAIT...> message displayed. About to start DMA and interrupt
controller test.
60 DMA page register test passed. To do DMA#1 base register test.
62 DMA#1 base register test passed. To do DMA#2 base register test.
65 DMA#2 base register test passed. To program DMA unit 1 and 2.
66 DMA unit 1 and 2 programming over. To initialize 8259 interrupt controller.
7F Extended NMI sources enabling is in progress.
80 Keyboard test started. Clearing output buffer, checking for stuck key, to issue keyboard reset
command.
81 Keyboard reset error/stuck key found. To issue keyboard controller interface test command.
82 Keyboard controller interface test over. To write command byte and init circular buffer.
83 Command byte written, global data init done. To check for lock-key.
84 Lock-key checking over. To check for memory size mismatch with CMOS.
85 Memory size check done. To display soft error and check for password or bypass setup.
86 Password checked. About to do programming before setup.
87 Programming before setup complete. To uncompress SETUP code and execute CMOS setup.
88 Returned from CMOS setup program and screen is cleared. About to do programming after setup.
89 Programming after setup complete. Going to display power-on screen message.
8B First screen message displayed. <WAIT...> message displayed. PS/2 Mouse check and
extended BIOS data area allocation to be done.
8C Setup options programming after CMOS setup about to start.
8D Going for hard disk controller reset.
8F Hard disk controller reset done. Floppy setup to be done next.
91 Floppy setup complete. Hard disk setup to be done next.
95 Init of different buses optional ROMs from C800 to start. (See Section 4.3 for details of different
buses.)
96 Going to do any init before C800 optional ROM control.
97 Any init before C800 optional ROM control is over. Optional ROM check and control will be
done next.
98 Optional ROM control is done. About to give control to do any required processing after optional
ROM returns control and enable external cache.
99 Any initialization required after optional ROM test over. Going to setup timer data area and printer
base address.
9A Return after setting timer and printer base address. Going to set the RS-232 base address.
9B Returned after RS-232 base address. Going to do any initialization before Coprocessor test.
9C Required initialization before Coprocessor is over. Going to initialize the Coprocessor next.
9D Coprocessor initialized. Going to do any initialization after Coprocessor test.
9E Initialization after Coprocessor test is complete. Going to check extended keyboard, keyboard ID
and num-lock.
A2 Going to display any soft errors.
A3 Soft error display complete. Going to set keyboard typematic rate.
A4 Keyboard typematic rate set. To program memory wait states.
A5 Going to enable parity/NMI.
A7 NMI and parity enabled. Going to do any initialization required before giving control to optional
ROM at E000.
A8 Initialization before E000 ROM control over. E000 ROM to get control next.
A9 Returned from E000 ROM control. Going to do any initialization required after E000 optional ROM
control.
AA Initialization after E000 optional ROM control is over. Going to display the system configuration.
AB Put INT13 module runtime image to shadow.
AC Generate MP for multiprocessor support (if present).
AD Put CGA INT10 module (if present) in Shadow.
AE Uncompress SMBIOS module and init SMBIOS code and form the runtime SMBIOS image in
shadow.
B1 Going to copy any code to specific area.
00 Copying of code to specific area done. Going to give control to INT-19 boot loader.
