IBM BIOS Post Codes - BIOS Central

CPU	Perform register test on the CPU by writing data patterns to the registers and reading the results of the write
ROM BIOS Checksum	The value of the bits inside the BIOS chip(s) is added to a preset value that should create a total value of 00
CMOS RAM	RAM within the CMOS chip is tested by writing data patters tot he area and verifying that the data was stored correctly
DMA	Test DMA chips by forcing control inputs to the CPU to an active state and verifying that the proper reactions occur
8042/8742 Keyboard Controller	Test including Gate A20 and the reset command. The buffer space is prepared and data is sent to the determined area via the keyboard controller to see if commands are received and executed correctly
Base 64K System RAM	Perform a walking bit test on the first 64K of RAM so the BIOS vector area can be initialized. Check for bad RAM chips or a data/address line
8259A PIC	Determine if commands to interrupt CPU processes are carried out correctly. Check the PIC, PIT, RTC, CMOS and Clock chips
8254 PIT	Check that proper setup and hold times are given to the PIC for interrupts of the CPU processes. Check the PIT or Clock chip
82385 Cache Controller	This is normally responsible for cache and shadow memory
CMOS RAM Configuration Data	Check information in CMOS RAM before further testing so any failures after this could also be down to the CMOS chip
CRT Controllers	Test any video adapters listed in the CMOS
RAM above 64K	perform walking bit pattern test on memory above 64K listed in CMOS
Keyboard	Test interface to the keyboard including scan code stuck keys etc.
Pointing Device	Test and initialize vector for any pointing devices found. Failure to see a device may be down to the device itself but there may be a problem with the CMOS or 8042/8742
Diskette Drive A:	Test and initialize the A: drive
Serial Interface Circuitry	Test any RS232 devices found at the proper I/O address
Diskette Controllers	In an A: drive has been found further testing is performed before proceeding to the bootloader. This test includes reading the first sector of any diskette in the drive to see if a valid boot code is there
Fixed Disk Controllers	Test and initialize any hard drives set in the CMOS including reading the first sector of the hard drive to see if a valid boot code exists

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IBM XT BIOS (Port 60):

00 or FF	CPU register test failed
01	BIOS ROM checksum failed
02	System timer 1 failed
03	8237 DMA register Read/Write failed
04	Base 32K RAM failed

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IBM AT BIOS:

01	CPU flag and register tested
02	BIOS ROM checksum tested
03	CMOS shutdown byte 0F tested
04	8254 PIT channel 0 tested
05	8254 PIT channel 1 tested
06	8237 DMA initialize registers test 0
07	8237 DMA initialize registers test 1
08	DMA page register tested
09	Memory refresh tested
0A	Soft reset tested
0B	8042 keyboard controller reset
0C	8042 keyboard controller reset OK
0D	8042 keyboard controller reset
0E	Memory tested
0F	I/P buffer switch settings obtained
DD	RAM error
11	Protected mode initialized
12	Protected mode registers tested
13	8259 PIC #2 initialized
14	Temporary Interrupt vectors setup
15	BIOS Interrupt vectors obtained
16	CMOS checksum and battery OK
17	Defective CMOS battery flag set
18	CMOS set checked
19	CMOS return address byte set
1A	Temporary stack set
1B	Segment address 01-0000, second 64K, tested
1C	Memory size; See if 512K or 640K present
1D	Segment address 10-000, over 640K, tested
1E	Expansion memory set as is reported by the CMOS
1F	Address lines 19-23 tested
20	Preparing to return to protected mode
21	Return from protected mode successful; 6845 video controller initialized and started
22	6845 video controller tested
23	EGA/VGA BIOS tested
24	8259PIC Read/Write mask register with 1's and 0's
25	Interrupt mask registers tested
26	Unexpected Interrupts checked for; Error 101 displayed
27	System board tested: POST logic
28	Unexpected NMI Interrupts tested for
29	8253 PIT timer tested
2A	8253 timer tested
2B	8253 timer initialized; System board error
2C	8253 timer Interrupt initialization; System board failure
2D	8042 keyboard controller checked for command
2F	8042 keyboard checked for warm boot
30	Shutdown return 2 set
31	Protected mode enabled
32	Address lines 0-15
33	Next block of 64K RAM tested
34	Real mode enabled
35	8042 keyboard controller tested
36	Check for keyboard error
38	8042 keyboard controller failed
3A	8042 keyboard controller initialized
3B	Expansion ROM's checked for in 2K blocks
3C	Floppy drive controller tested
3D	Initialize the floppy drive controller
3E	Initialize hard disk controller
3F	Initialize parallel port
40	Hardware Interrupt enabled
41	System code at segment E0000h checked for
42	Exit to system code
43	Call to boot loader
44	Boot from fixed disk
45	Unable to boot from fixed disk; Boot to BASIC
81	Descriptor table built
82	Virtual mode started
90-B6	Memory and bootstrap testing done
F0	Data segment set
F2	Interrupts tested
F1	Exception Interrupts tested
F3	Verify 286 protected mode instructions (LDT/SDT and LTR/STR)
F4	Verify 286 protected mode instructions (Bound instruction)
F5	Verify 286 protected mode instructions (Push and pop)
F6	Verify 286 protected mode instructions (Access rights)
F7	Verify 286 protected mode instructions (RPL field adjusted)
F8	Verify 286 protected mode instructions (LAR function)
F9	Verify 286 protected mode instructions (LSL instruction)
FA	Verify 286 protected mode instructions (Memory chip selected)

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IBM PS/2 (Micro Channel) BIOS:

00	CPU tested with patter FFAA0055
01	CPU 32 register tested
02	BIOS ROM checksum tested
03	System port 94 enabled and checked
04	POST registers, port 102 enabled and checked
05	POST registers port 96 enabled and tested
06	CMOS shutdown byte 0F tested
07	CMOS extended port 74-76 enabled and tested
08	DMA and page registers tested (ports 2, 18, 1A and 1C)
09	DMA initialized
0A	Memory refresh tested
0B	8042 keyboard controller buffers tested (ports 61 and 64)
0C	8042 keyboard controller internal test (port 60)
0D	8042 keyboard controller internal test continued
0E	8042keyboard controller self test error
0F	Memory sized and setup
10	First 512K base memory tested
11	Base memory error, system halted
12	Protected mode instructions tested; Keyboard commands tested
13	PIC Interrupt controller 1 (master) tested
14	PIC Interrupt controller 2 (slave) tested
15	Initialize 120 Interrupt vectors
16	Initialize 16 extended vectors
17	CMOS/RTC tested; CMOS byte 0D tested
18	CMOS/RTC checksum tested
19	CMOS/RTC battery tested
1A	Check for soft or hard reset
1B	Protected mode initialization
1C	Protected mode stack set; Pointer to end of first 64K set
1D	Low memory size tested in protected mode
1E	Memory size information saved
1F	Memory split address setup
20	Check for extended memory beyond 64MB
21	Test memory-address bus lines
22	Clear parity error and channel lock
23	Initialize interrupt 0
24	Check CMOS RAM validity
25	Write keyboard-controller command byte
40	Check valid CMOS RAM and video system
41	Display error code 160
42	Test registers in both interrupt controllers
43	Test interrupt controller registers
44	Test interrupt mask registers
45	Test NMI
46	NMI error has been detected
47	Test system timer 0
48	Check system speaker clock
49	Test system timer 0 count
4A	Test system timer 1 count
4B	Check if timer interrupt occurred
4C	Test timer 0 for improper operation (too fast or too slow)
4D	Verify timer interrupt 0
4E	Check 8042 keyboard controller
4F	Check for soft reset
50	Prepare for shutdown
51	Start protected mode test
52	Test memory in 64KB increments
53	Check if memory test done
54	Return to real mode
55	Test for regular or manufacturing mode
56	Disable the keyboard
57	Check for keyboard self test
58	Keyboard test passed
59	Test the keyboard controller
5A	Configure the mouse
5B	Disable the mouse
5C	Initialize interrupt vectors
5D	Initialize interrupt vectors
5E	Initialize interrupt vectors
60	Save DDNIL status
61	Reset floppy drive
62	Test floppy drive
63	Turn floppy-drive motor off
64	Set up serial ports
65	Enable real time clock interrupt
66	Configure floppy drives
67	Configure hard drives
68	Enable system CPU arbitration
69	Scan for adapter ROM's
6A	Verify serial and parallel ports
6B	Set up equipment byte
6C	Set up configuration
6D	Set keyboard-typematic rate
6E	Call Int. 19 boot loader

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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.