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IBM AT BIOS / Motherboard POST Error Codes

QuickPOST SeriesPOST Error CodesUpdated 6/14/2019
Code Meaning
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)