BIOS from 1991 - Present
The red indicates a motherboard with BIOS from 1991 to the present

NMI Disable NMI interrupt line to the CPU is disabled by setting bit 7 I?O port 70h (CMOS)
Power On Delay Once the keyboard controller gets power, it sets the hard and soft reset bits.  Check the keyboard controller or clock generator if a failure occurs
Initialize Chipsets Check the BIOS, CLOCK and chipsets
Reset Determination The BIOS reads the bits in the keyboard controller to see if a hard or soft reset is required (a soft reset will not test memory above 64K).  Failure could be the BIOS or keyboard controller
ROM BIOS Checksum The BIOS performs a checksum on itself and adds a preset factory value that should make it equal to 00.  If a failure occurs, check the BIOS chips
Keyboard Test A command is sent to the 8042 keyboard controller which performs a test and sets a buffer space for commands.  After the buffer is defined the BIOS sends a command byte, writes data to the buffer, checks the high order bits of the internal keyboard controller and issues a No Operation (NOP) command
CMOS Shutdown byte in CMOS RAM offset 0F is tested, the BIOS checksum calculated and diagnostic byte 0E updated before the CMOS RAM area is initialized and updated for date and time.  Check the RTC and CMOS chip or battery if a failure occurs
DMA (8237) and PIC (8259) Disable The DMA and Programmable Interrupt Controller are disabled before the POST proceeds and further.  Check the 8237 or 8259 chips if a failure occurs
Video Disable The video controller is disabled and port B initialized.  Check the video adapter if a failure occurs
Chipset Initialized and Memory Detected Memory addressed in 64K blocks.   Failure would be in the chipset.  If all memory is not seen, failure could be in a chip in the block after the last one seen
PIT Test The timing functions of the 8254 Programmable Interrupt Timer are tested.  The PIT and RTC chips normally cause errors here
Memory Refresh PIT's ability to refresh memory is tested.  If an XT, DMA controller #1 handles this.  Failure is normally the PIT (8254) in AT's or the 8237, DMA #1, in XT's
Address Line Test the address lines in the first 64K of RAM.  If a failure occurs, an address line may be the problem
Base 64K Data patterns are written to the first 64K of RAM, unless there is a bad RAM chip in which case you will get a failure
Chipset Initialization The PIT, PIC and DMA controllers are initialized
Set Interrupt Table Interrupt vector table used by PIC is installed in low memory, the first 2K
8042 Keyboard Controller Check The BIOS reads the buffer area in the keyboard controller I/O port 60.  Failure here is normally the keyboard controller
Video Tests The type of video adapter is checked for, then a series of tests are performed on the adapter and monitor
BIOS Data Area The vector table is checked for proper operation and video memory verified before protected mode tests are entered into.   This is done so that any errors found are displayed on the monitor
Protected Mode Tests Perform reads and writes to all memory locations below 1MB.  Failure at this point indicate a bad RAM chip, the 8042 Keyboard Controller or a data line
DMA Chips The DMA registers are tested using a data pattern
Final Initialization these differ with each version.   Typically, the floppy and hard drives are tested and initialized and a check is made for serial and parallel devices.  The information gathered is then compared against the contents of the CMOS and you will see the results of any failures on the monitor
BOOT The BIOS hands over control to the Int 19 bootloader.  This is where you would see error messages such as non-system disk

AMIT BIOS Post Codes (Prior to April 1990)

01 NMI is disabled and the i286 register test is about to start
02 i286 register test has passed
03 ROM BIOS checksum test (32Kb from F8000h) passed OK
04 8259 programmable interrupt controller has initialized OK
05 CMOS interrupt disabled
06 Video system disabled and the system timer checks OK
07 8253/4 programmable-interval timer test OK
08 Delta counter channel 2 OK
09 Delta counter channel 1 OK
0A Delta counter channel 0 OK
0B Parity status cleared
0C The refresh and system timer check OK
0D Refresh check OK
0E Refresh period checks OK
10 Ready to start 64KB base memory test
11 Address line test OK
12 64KB base memory test OK
13 System-interrupt vectors initialized
14 8042 keyboard controller checks OK
15 CMOS read/write test OK
16 CMOS checksum and battery OK
17 Monochrome video mode OK
18 CGA color mode set OK
19 Attempting to pass control to video ROM at C0000h
1A Returned from video ROM
1B Display memory read/write test OK
1C Display memory read/write alternative test OK
1D Video retrace test OK
1E Global equipment byte set for proper video operation
1F Ready to initialize video system
20 Video test OK
21 Video display OK
22 The power-on message is displayed
30 Ready to start the virtual-mode memory test
31 virtual memory mode test started
32 CPU has switched to virtual mode
33 Testing the memory address lines
34 Testing the memory address lines
35 Lower 1MB of RAM found
36 Memory size computation checks OK
37 Memory test in progress
38 Memory below 1MB is initialized
39 Memory above 1MB is initialized
3A Memory size is displayed
3B Ready to test the lower 1MB of RAM
3C Memory test of lower 1MB OK
3D Memory test above 1MB OK
3E Ready to shutdown for real-mode testing
3F Shutdown OK- now in real mode
40 Ready to disable gate A20
41 A20 line disabled successfully
42 Ready to start DMA controller test
4E Address line test OK
4F System still in real mode
50 DMA page register test OK
51 Starting DMA controller 1 register test
52 DMA controller 1 test passed, starting DMA controller 2 register test
53 DMA controller 2 test passed
54 Ready to test latch on DMA controller 1 and 2
55 DMA controller 1 and 2 latch test OK
56 DMA controller 1 and 2 configured OK
57 8259 programmable interrupt controller initialized OK
58 8259 programmable interrupt controller mask register OK
59 Master 8259 programmable interrupt controller mask register OK
5A Ready to check timer interrupts
5B Timer interrupt check OK
5C Ready to test keyboard interrupt
5D Error detected in timer or keyboard interrupt
5E 8259 programmable interrupt controller error
5F 8259 programmable interrupt controller OK
70 Start of keyboard test
71 Keyboard controller Ok
72 Keyboard tested OK
73 Keyboard global initialization OK
74 Floppy setup ready to start
75 Floppy controller setup OK
76 Hard disk setup ready to start
77 Hard disk controller setup OK
79 Ready to initialize timer data
7A Verifying CMOS battery power
7B CMOS battery verified OK
7D Analyzing CMOS RAM size
7E CMOS memory size updated
7F Send control to adapter ROM
80 Enable the setup routine if <Delete> is pressed
82 Printer data initialization is OK
83 RS-232 data initialization is OK
84 80x87 check and test OK
85 Display any soft-error message
86 Give control to ROM E0000h
87 Return from system ROM
00 Call the Int19 boot loader

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