AT&T BIOS Post Codes - BIOS Central

01	CPU test
02	System I/O port test
03	ROM checksum test
05	DMA page register test
06	Timer 1 test
07	Timer 2 test
08	RAM refresh test
09	8/19 bit bus conversion check
0A	Interrupt controller 1 test
0B	Interrupt controller 2 test
0C	Keyboard controller test
0D	CMOS RAM/RTC test
0E	Battery power test
0F	CMOS RAM checksum test
10	CPU protected mode
11	Display configuration test
12	Display controller test
13	Primary display error
14	Extended CMOS test
15	AT bus reset
16	Initialize chipset registers
17	Check for extension ROM's
18	Internal memory address test
19	Remap memory
1A	Memory interleave mode test
1B	Remap shadow memory
1C	Setup MRAM
1D	Expanded memory test
1E	AT memory error
1F	Internal memory error
20	Minimum POST tests complete
21	DMA controller 1 test
22	DMA controller 2 test
23	Timer 0 test
24	Initialize internal controllers
25	Unexpected interrupt
26	Expected interrupt
30	Switch to protected mode
31	Size AT bus memory or size external memory
32	Address lines A16 to A23 test
33	Internal memory test or conventional memory test
34	AT bus memory test or external memory test
38	Shadow ROM BIOS to RAM
39	Shadow extension BIOS to RAM
40	Enable/disable keyboard
41	Keyboard clock and data test
42	Keyboard reset
43	Keyboard controller test
44	A20 gate test
50	Initialize interrupt table
51	Enable timer interrupt
60	Floppy controller/drive test
61	Hard disk controller test
62	Initialize floppy drives
63	Initialize hard drives
70	Real time clock test
71	Set real time clock
72	Test parallel interfaces
73	Test serial interfaces
74	Check external ROM's
75	Numeric coprocessor test
76	Enable keyboard and RTC interrupts (IRQ 9)
F0	Display system startup message
F1	Check for ROM at E000h
F2	Boot from floppy or hard disk
F3	Run setup program
F4	Run password program
FC	DRAM type detection
FD	CPU register test

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AT&T BIOS Post Codes v3.0:

01	CPU test 1: verify CPU status bits
02	Powerup check - Initialize motherboard and chipset with default values; Check 8042 keyboard controller buffer
03	Clear 8042 keyboard controller - send command AA, fail if status is not 2 output buffer full
04	Reset 8042 keyboard controller
05	Get8042 keyboard controller manufacturing status
06	Initialize motherboard chipset; disable color/mono video; disable 8237 DMA controller; reset 80x87 coprocessor; initialize 8255 timer 1; clear DMA/page registers/CMOS RAM shutdown byte
07	CPU test 2; read/write/verify CPU registers SS, SP, BP, with FF and 00
08	Initialize CMOS RAM/RTC
09	Checksum 32K of BIOS ROM
0A	Initialize video interface; initialize 6845 controller
0B	Test 8254 programmable interrupt timer channel 0
0C	Test 8254 programmable interrupt timer channel 1
0D	Test 8254 programmable interrupt timer channel 2
0E	Test CMOS RAM shutdown byte
0F	Test extended CMOS RAM, if present
10	Test 8237 DMA controller channel 0
11	Test 8237 DMA controller channel 1
12	Test 8237 DMA controller page registers
13	Test 8741 keyboard controller interface
14	Test memory refresh toggle
15	Test first 64K of base memory
16	Set up interrupt tables in low memory
17	Set up video I/O operations
18	(1 beep) Test MDA/CGA video memory unless EGA/VGA adapter is found
19	Test 8259 programmable interrupt timer channel 1
1A	Test 8259 programmable interrupt timer channel 0
1B	Test CMOS RAM battery level
1C	Test CMOS RAM checksum
1D	Set system memory size parameters
1E	Size base memory 64K at a time
1F	Test base memory found from 64K to 640K
20	Test stuck bit in 8259 programmable interrupt controller
21	Test for stuck NMI bits
22	Test 8259 programmable interrupt controller functionality
23	Test protected mode
24	Size extended memory above 1MB
25	Test all base and extended memory found, except the first 64K
26	Test protected mode exceptions
27	Initialize shadow RAM and move system BIOS and/or video BIOS into it if enabled by CMOS RAM setup
28	Detect and initialize Intel 8242/8248 chip
29	Reserved
2A	Detect and initialize keyboard
2B	Detect and initialize floppy drive
2C	Detect and initialize serial ports
2D	Detect and initialize parallel ports
2E	Detect and initialize hard drive
2F	Detect and initialize coprocessor
30	Reserved
31	Detect and initialize adapter ROM's
BD	Initialize Orvonton cache controller, if present
CA	Initialize 386 Micronics cache, if present
CC	Shutdown NMI handler
EE	Test for unexpected processor exception
FF	Interrupt 19 boot loader

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AT&T BIOS Post Codes v3.00 - 3.03 8/26/87 286 N3.03 Extensions:

01	Processor test #1
02	Determine type of POST test
03	Clear 8042 keyboard controller interface
04	Reset 8042 keyboard controller interface
05	Get 8042 keyboard controller manufacturing status
06	Initialize LSI onboard chips
07	Processor test #2
08	Initialize CMOS chip
09	EPROM checksum for 32KB
0A	Initialize video interface
0B	Test 8254 programmable interrupt timer channel 0
0C	Test 8254 programmable interrupt timer channel 1
0D	Test 8254 programmable interrupt timer channel 2
0E	Test CMOS date and timer
0F	Test CMOS shutdown byte
10	Test DMA channel 0
11	Test DMA channel 1
12	Test DMA page registers
13	Test 8741 keyboard controller
14	Test memory refresh toggle circuits
15	Test 1st 64KB of system memory
16	Setup interrupt vector table
17	Setup video I/O operations
18	Test video memory
19	Test 8259 programmable interrupt controller channel 1 mask bits
1A	Test 8259 programmable interrupt controller channel 2 mask bits
1B	Test CMOS battery level
1C	Test CMOS checksum
1D	Setup configuration byte for CMOS
1E	Sizing system memory & compare with CMOS
1F	Test found system memory
20	Test stuck 8259's interrupt bits
21	Test stuck NMI bits
22	Test 8259 programmable interrupt controller functionality
23	Test protected mode and A20 gate
24	Sizing extended memory above 1MB
25	Test found system/extended memory
26	Test exceptions in protected mode
27	Reserved
2A	POST_KEYBOARD
2B	POST_FLOPPY
2C	POST_COMM
2D	POST_PRN
2E	POST_DISK
2F	POST_MATH
30	POST_EXCEPTION
CC	POST_NMI

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AT&T BIOS Post Codes XT 8088/86 BIOS v3.1:

01	Processor test 1
02	Determine type of POST test
06	Initialize 8259 programmable interrupt controller and 8237 DMA controller chips
07	Processor test #2
09	EPROM checksum for 32KB
0A	Initialize video controller 6845 registers
15	Test 1st 64K of system memory
16	Setup interrupt vector table in 1st 64K
17	Setup video I/O operations
18	Test video memory
19	Test 8259 programmable interrupt controller channel 1 mask bits
1A	Test 8259 programmable interrupt controller channel 2 mask bits
1D	Setup configuration byte from CMOS
1E	Sizing system memory & compare with CMOS
1F	Test found system memory
20	Test stuck 8259's interrupt bits
21	Test stuck NMI bits
22	Test 8259 interrupt functionality
2A	Initialize keyboard
2B	Initialize floppy controller and drive
2C	Initialize COM ports
2D	Initialize LPT ports
2F	Initialize coprocessor
31	Initialize option ROM's
FF	Interrupt 19 boot loader

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AT&T BIOS Post Codes 386 BIOS 3.1:

01	Processor test 1
02	Determine POST type
03	Clear 8042 keyboard controller interface
04	Reset 8042 keyboard controller interface
05	Get 8042 keyboard controller manufacturing status
06	Initialize onboard LSI chips
07	Processor test 2
08	Initialize CMOS timer/real time clock
09	EPROM checksum
0A	Initialize video interface
0B	Test 8254 programmable interrupt timer channel 0
0C	Test 8254 programmable interrupt timer channel 1
0D	Test 8254 programmable interrupt timer channel 2
0E	Test CMOS shutdown byte
0F	Test extended CMOS
10	Test DMA channel 0
11	Test DMA channel 1
12	Test DMA page registers
13	Test keyboard controller interface
14	Test memory refresh toggle circuits
15	Test first 64KB of system memory which is used by system BIOS
16	Setup interrupt vector table
17	Video I/O operations
18	Video memory test for CGA and mono cards
19	Test 8259 mask bits on channel 1
1A	Test 8259 mask bits on channel 2
1B	Check CMOS battery level
1C	Test the CMOS checksum data at 2E and 2Fh
1D	Configuration of CMOS if checksum good
1E	System memory size determined
1F	Tests memory from the top of 64K to the top of memory
20	Check for stuck 8259 interrupt bits
21	Check for stuck NMI interrupt bits
22	Check for 8259 functionality
23	Verifies protected mode
24	System memory size is determined for extended memory
25	Tests extended memory found above using virtual 8086 paging mode and writing an FFFF/AA55/0000 pattern
26	Protected mode exceptions
27	Test cache controller(386/486) or shadow RAM
28	Set up cache controller or 8042 keyboard controller
29	Reserved
2A	Initialize keyboard and controller
2B	Initialize floppy drive and controller
2C	Detect and initialize serial ports
2D	Detect and initialize parallel ports
2E	Initialize hard drive and controller
2F	Detect and initialize coprocessor
30	Reserved
31	Detect and initialize option ROM's
3B	Initialize secondary cache with Opti chipset (486 only)
CC	NMI handler shutdown
EE	Unexpected processor exception
FF	Interrupt 19 boot loader

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AT&T BIOS Post Codes ISA/EISA BIOS v4.0:

01	Processor test 1
02	Processor test 2
03	Calculate BIOS EPROM
04	Test CMOS RAM interface
05	Initialize chipset
06	Test memory refresh
07	Setup low memory
08	Setup interrupt vector table
09	Test CMOS RAM checksum and load default
0A	Initialize keyboard
0B	Initialize video interface
0C	Test video memory
0D	OEM specific; initialization of motherboard chips required by OEM
0E	Reserved
0F	Test DMA controller 0
10	Test DMA controller 1
11	DMA page registers
12	Reserved
13	Reserved
14	Test 8254 timer 0 counter 2
15	Verify 8259 programmable interrupt controller channel 1
16	Verify 8259 programmable interrupt controller channel 2
17	Test for stuck 8259 interrupt bits
18	Test 8259 functionality
19	Test for NMI bits
1A	Reserved
1B	Reserved
1C	Reserved
1D	Reserved
1E	Reserved
1F	Set EISA mode
20	Initialize and enable EISA slot 0
21	Initialize and enable EISA slot 1
22	Initialize and enable EISA slot 2
23	Initialize and enable EISA slot 3
24	Initialize and enable EISA slot 4
25	Initialize and enable EISA slot 5
26	Initialize and enable EISA slot 6
27	Initialize and enable EISA slot 7
28	Initialize and enable EISA slot 8
29	Initialize and enable EISA slot 9
2A	Initialize and enable EISA slot 10
2B	Initialize and enable EISA slot 11
2C	Initialize and enable EISA slot 12
2D	Initialize and enable EISA slot 13
2E	Initialize and enable EISA slot 14
2F	Initialize and enable EISA slot 15
30	Size base memory from 256K to 640K and test
31	Test extended memory
32	If EISA mode flag set, test EISA memory found during slot initialization
33	Reserved
34	Reserved
35	Reserved
36	Reserved
37	Reserved
38	Reserved
39	Reserved
3A	Reserved
3B	Reserved
3C	Verify CPU can switch in and out of protected, virtual 86 and 8086 page modes
3D	Check for mouse and initialize if present
3E	Initialize cache controller
3F	Enable shadow RAM
40	Reserved
41	Initialize floppy drive controller and drives
42	Initialize hard drive controller and hard drives
43	Serial ports detected and initialized
44	Parallel ports detected and initialized
45	Coprocessor detected and initialized
46	Setup message print to screen
47	Boot speed set
48	Reserved
49	Reserved
4A	Reserved
4B	Reserved
4C	reserved
4D	Reserved
4E	If manufacturing POST loop pin set, reboot, otherwise non-fatal error messages will be displayed
4F	Security check
50	Write all CMOS values back to CMOS RAM
51	Preboot enabled
52	Initialize ROM's between C80000-EFFFF
53	Initialize time value at address 40 of BIOS
55	Initialize DDNIL counter to NULL's
63	Boot attempt
B0	Spurious interrupt occurred in protected mode
B1	Unclaimed NMI
BF	Program chipset
C0	OEM specific
C1	OEM specific
C2	OEM specific
C3	OEM specific
C4	OEM specific
C5	OEM specific
C6	OEM specific
C7	OEM specific
C8	OEM specific
C9	OEM specific
D0	Debug
D1	Debug
D2	Debug
D3	Debug
D4	Debug
D5	Debug
D6	Debug
D7	Debug
D8	Debug
D9	Debug
DA	Debug
DB	Debug
DC	Debug
DD	Debug
DE	Debug
DF	Debug
E0	Reserved
E1	Setup page 1
E2	Setup page 2
E3	Setup page 3
E4	Setup page 4
E5	Setup page 5
E6	Setup page 6
E7	Setup page 7
E8	Setup page 8
E9	Setup page 9
EA	Setup page 10
EB	Setup page 11
EC	Setup page 12
ED	Setup page 13
EE	Setup page 14
EF	Setup page 15
FF	Boot via interrupt 19 if no errors detected

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AT&T BIOS Post Codes EISA BIOS:

01	CPU flags
02	CPU registers
03	Initialize DMA
04	Memory refresh
05	Keyboard initialization
06	ROM checksum
07	CMOS
08	256K memory
09	Cache
0A	Set interrupt table
0B	CMOS checksum
0C	Keyboard initialization
0D	Video adapter
0E	Video memory
0F	DMA channel 0
10	DMA channel 1
11	DMA page register
14	Timer chip
15	Programmable interrupt controller 1
16	Programmable interrupt controller 2
17	programmable interrupt controller stuck bits
18	Programmable interrupt controller maskable IRQ's
19	NMI bit check
1F	CMOS RAM
20	Slot 0
21	Slot 1
22	Slot 2
23	Slot 3
24	Slot 4
25	Slot 5
26	Slot 6
27	Slot 7
28	Slot 8
29	Slot 9
2A	Slot 10
2B	Slot 11
2C	Slot 12
2D	Slot 13
2E	Slot 14
2F	Slot 15
30	Memory size 256K
31	Memory test over 256K
32	EISA memory
3C	CMOS setup on
3D	Mouse
3E	Cache RAM
3F	Shadow RAM
40	N/A
41	Floppy drive
42	Hard drive
43	Serial and parallel ports
45	coprocessor
47	Speed
4E	manufacturing loop
4F	Security
50	CMOS update
51	Enable NMI
52	Adapter ROM's
53	Set time
63	Boot
B0	NMI in protected
B1	Disable NMI
BF	Chipset program
C0	Cache on/off
C1	Memory size
C2	Base 256K test
C3	DRAM page select
C4	Video switch
C5	Shadow RAM
C6	Cache program
C8	Speed switch
C9	Shadow RAM
CA	OEM chipset
FF	Boot

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AT&T BIOS Post Codes late Award BIOS v4.5x-non PnP:

C0	Turnoff chipset cache
01	Processor test 1
02	Processor test 2
03	Initialize chipset; Disable NMI/PIE/UEL/SQWV, video, parity checking, DMA; Reset coprocessor; Clear all page registers and CMOS shutdown byte; Initialize timer 0, 1 and 2 including EISA timer to known state; Initialize DMA controllers 0 and 1; Initialize interrupt controllers 0 and 1 and EISA extended controllers
04	Test memory refresh
05	Blank video
06	Reserved
07	Test CMOS and battery status
C1	Memory presence test
C5	Early shutdown
C6	Cache presence test
08	Setup low memory
09	Early cache initialization
0A	Setup interrupt vector table; Initialize first 120 interrupt vectors with SPURIOUS_INT_HDLR and initialize interrupts 00-FF according to INT_TBL
0B	Test CMOS RAM checksum
0C	Initialize keyboard
0D	Initialize video interface
0E	Test video memory
0F	Test DMA controller 0
10	Test DMA controller 1
11	Test DMA page registers
12	Reserved
13	Reserved
14	Test 8254 timer 0 counter 2
15	Test 8259 1 mask bits
16	Test 8259 2 mask bits
17	Test for 8259 stuck interrupt bits
18	Test 8259 interrupt functionality
19	Test for stuck NMI bits
1A	Display CPU clock
1B	Reserved
1C	Reserved
1D	Reserved
1E	Reserved
1F	Set EISA mode
20	Enable slot 0
21	Enable slot 1
22	Enable slot 2
23	Enable slot 3
24	Enable slot 4
25	Enable slot 5
26	Enable slot 6
27	Enable slot 7
28	Enable slot 8
29	Enable slot 9
2A	Enable slot 10
2B	Enable slot 11
2C	Enable slot 12
2D	Enable slot 13
2E	Enable slot 14
2F	Enable slot 15
30	Size base and extended memory
31	Test base and extended memory
32	Test EISA extended memory
33	Reserved
34	Reserved
35	Reserved
36	Reserved
37	Reserved
38	Reserved
39	Reserved
3A	Reserved
3B	Reserved
3C	Setup enabled
3D	Check for and initialize mouse if present
3E	Setup cache controller
3F	Reserved
BF	Chipset initialization
40	Display virus protect enable or disable
41	Initialize floppy controller and drive's
42	Initialize hard drive controller and drive's
43	Serial and parallel ports detected and initialized
44	Reserved
45	Coprocessor detected and initialized if present
46	Reserved
47	Reserved
48	Reserved
49	Reserved
4A	Reserved
4B	Reserved
4C	Reserved
4D	Reserved
4E	Manufacturing POST loop/display messages
4F	Security check
50	Write CMOS
51	Preboot enable
52	Initialize options ROM's between C800 and EFFF
53	Initialize time value in 40h BIOS area
60	Setup virus protect
61	Set boot speed
62	Setup numlock
63	Boot attempt
B0	Spurious if interrupt occurs in protected mode
B1	Unclaimed NMI
E1	Setup page 1
E2	Setup page 2
E3	Setup page 3
E4	Setup page 4
E5	Setup page 4
E6	Setup page 5
E7	Setup page 6
E8	Setup page 7
E9	Setup page 8
EA	Setup page 9
EB	Setup page 10
EC	Setup page 11
ED	Setup page 12
EE	Setup page 13
EF	Setup page 14
FF	Boot from interrupt 19

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AT&T BIOS Post Codes late Award BIOS v4-5x PnP:

C0	Turn off OEM specific cache; Initialize standard devices: DMA controller (8237), Programmable interrupt controller (8259), Programmable interval timer (8254), RTC chip
C1	Auto detection on onboard DRAM & cache
C3	Test first 256K DRAM
C5	Copy the BIOS from ROM into E000FFFF shadow RAM
01	Reserved
02	Reserved
03	Initialize EISA registers
04	Reserved
05	Keyboard controller setup; enable keyboard interface
06	Reserved
07	Verifies CMOS basic read/write functionality
BE	Program default values into chipset according to the MODBINable Chipset Default Table
09	Program configuration register for Cyrix CPU according to MODBINable Cyrix Register Table; OEM specific cache initialization
0A	Initialize first 32 interrupt vectors; Issue CPUID instruction to identify CPU type
0B	Verify RTC; Detect bad battery; Read CMOS data into BIOS stack area; PnP initializations (PnP BIOS only): Assign CSN to PnP ISA card, create resource map from ESCD; Assign I/O and memory for PCI devices (PCI BIOS only)
0C	Initialize BIOS data area
0D	Program chipsets value; Measure CPU speed for display; Video initialization (If no display, speaker beeps)
0E	Initialize APIC (multiprocessor BIOS only); Test video RAM; Show display message
0F	DMA channel 0 test
10	DMA channel 1 test
11	DMA page registers test
12	Reserved
13	Reserved
14	Test 8254 timer 0 counter 2
15	Test 8259 interrupt mask bits for channel 1
16	Test 8259 interrupt mask bits for channel 2
17	Reserved
19	Test 8259 functionality
1A	Reserved
1B	Reserved
1C	Reserved
1D	Reserved
1E	Execute EISA initialization if NVM is good
1F	Reserved
20	Reserved
21	Reserved
22	Reserved
23	Reserved
24	Reserved
25	Reserved
26	Reserved
27	Reserved
28	Reserved
29	Reserved
30	Size base and extended memory
31	Test base memory from 256K to 640K; Test extended memory from 1MB to the top of memory
32	Display Award Plug & Play BIOS Extension message; Program super I/O chipset
33	Reserved
34	Reserved
35	Reserved
36	Reserved
37	Reserved
38	Reserved
39	Reserved
3A	Reserved
3B	Reserved
3C	Set flag to allow access to CMOS setup
3D	Initialize keyboard; Initialize PS/2 mouse
3E	Initialize L2 cache
3F	Reserved
40	Reserved
BF	Program chipset values according to setup
41	Initialize floppy controller and floppy drives
42	Initialize hard drive controller and hard drives
43	initialize serial and parallel ports in PnP BIOS
44	Reserved
45	Initialize coprocessor
46	Reserved
47	Reserved
48	Reserved
49	Reserved
4A	Reserved
4B	Reserved
4C	Reserved
4D	Reserved
4E	Error messages displayed if detected (F1 displayed to continue)
4F	Ask for password if needed; Energy star logo displayed if Green BIOS
50	Write all CMOS values currently in the BIOS stack back to the CMOS
51	Reserved
52	Initialize ISA ROM's; Assign IRQ's to any PCI devices, initialize PCI ROM's; PnP initializations; Shadow RAM setup; Parity setup; Power management initialized
53	Serial and parallel ports initialized for non-PnP BIOS
54	Reserved
55	Reserved
56	Reserved
57	Reserved
58	Reserved
59	Reserved
5A	Reserved
5B	Reserved
5C	Reserved
5D	Reserved
5E	Reserved
5F	Reserved
50	Virus protection setup for boot sector if enabled
61	L2 cache enabled; Boot up speed according to setup; Chipset initialization finalized; Power Management finalized; Show system configuration table
62	Setup time/date according to setup values; Program the numlock, typematic rates, and typematic speeds according to setup
63	ESCD updated if changed to BIOS made; Clear memory that may be used; Bot from interrupt 19
FF	Boot

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All information has been gathered with permission of the respective BIOS providers. Although Bios Central has used reasonable effort to ensure accuracy we are unable to verify all codes posted. Use at your own risk. Bios Central, or any person associated with Bios Central takes no responsibility for any dmage resulting from the use of this information.