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BIOS PostCodes

Intel Motherboards:

  • Chips & Technologies Post Procedures
  • Chips & Technologies BIOS Post Codes


Some are sent to the display in decimal as well as port address 80h.  Micro Channel BIOS's use port 680 and 3BC.

Chips & Technologies Post Procedures:

Power on tests CPU synchronizes with clock.  Check the CPU or clock if a failure occurs
System ROM Check The BIOS runs a checksum on itself.   Check the BIOS chips if a failure occurs
DMA controller Fail DMA controllers are initialized and tested.  Check the DMA chips if a failure occurs
System Timer Failed Channels 0, 1, and 2 are tested in sequence.  If a failure occurs, check the PIT chips
Base 64K Memory Testing Walking bit test performed on first 64K of RAM which is critical for the BIOS vector area to be initialized.  Check for bad RAM chips or a bad data or address line
Interrupt Controller Failed Test the 8259 chip
CPU Still In Protected Mode Attempts are made to read the configuration of the system through the 8042 keyboard controller
Refresh Not Occurring Memory refresh is tested; standard refresh is 120-140ns.  Check the PIT if a failure occurs
Keyboard Controller Not Responding Tests are run on the keyboard controller.  the the KBC 8042 if a failure occurs
Could Not Enter Protected Mode BIOS attempts to enter protected mode to test extended memory.  Check the 8042 KBC chip or the A20 gate address line if a failure occurs
Initialize Timer Attempts are made to initialize the PIT
Initialize DMA Controller Attempts are made to initialize the DMA controllers
Entering/Exiting Protected Mode The translation is handled by the keyboard controller and the A20 gate address line.  Check the keyboard controller if a failure occurs
Relocate Shadow RAM BIOS attempts to shadow itself into extended memory.  Check for memory problems if a failure occurs
Test For EMS Check for EMS adapter or an improper CMOS setting/Jumper setting if a failure occurs
Test Video Capabilities Normally includes a memory test on the adapter memory up to 256K
Test Memory Extensive testing of Base, Extended,and Expanded memory.  Check for defective memory modules, 8042 KBC, A20 gate address line or an improper CMOS and/or jumper setting
Check System Options The hardware in the system is compared with the values stored in CMOS.  The PIT, PIC, 8042 KBC, RTC and other system board components are tested again
Peripheral Check and test Checks are made for the peripherals at standard I/O ports including serial and parallel ports, keyboards, and math coprocessor.   You should see an error message on screen at the point if a failure occurs
Floppy Test Floppy devices set in CMOS are checked and initialized.  If a bootable floppy is found the fixed disks are tested and the BIOS will boot to the floppy disk.  Check for defective controllers or an improper CMOS Setup if a failure occurs
Fixed Disk Test Checks for fixed disks in CMOS.  If no bootable floppy in the A: drive, then the BIOS loads the first sector off the first fixed disk and jumps to the area of memory where the sector was loaded.  You may just see a flashing cursor or an error message from the potential operating system.  Check for improper CMOS Setup, defective controller, or fixed disk failure.  Also, check for a corrupt bootloader on the fixed disk
Advanced Options These include the mouse, cache, etc..   you should see an error message on the screen at this point, except that a defective cache may hang the system.  In most cases, the cache will be disabled by the BIOS

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Chips & Technologies BIOS Post Codes:

00 Error in POS register
01 CPU flag register failed
02 CPU register test failed
03 BIOS ROM checksum failed
04 DMA controller test failed
05 System timer IC failed
06 Base 64K RAM failed address test: not installed, misconfigured, or bad addressing
07 Base 64K RAM failed data test
08 Interrupt controller failed
09 Hot (unexpected) interrupt occurred
0A System timer does not interrupt
0B CPU still in protected mode
0C DMA page registers failed
0D Refresh not occurring
0E Keyboard controller not responding
0F Could not enter protected mode
10 GDT or IDT failed, Keyboard controller failed
11 LDT register failed, Keyboard controller failed
12 Task register failed, Keyboard controller failed
13 LSL instruction failed, keyboard controller failed
14 LAR register failed, Keyboard controller failed
15 VERR/VERW failed, Keyboard controller failed
16 Keyboard controller gate A20 failed
17 Exception failed/unexpected exception
18 Shutdown during memory test
19 Last used error code
1A Copyright checksum error
1B Shutdown during memory sizing
1C Chipset initialization
50 Initialize hardware
51 Initialize timer
52 Initialize DMA controller
53 Initialize 8259 programmable interrupt controller
54 Initialize system chipset
55 Setup EMS configuration
56 Entering protected mode for first time
57 Size memory chips
58 Configure memory chip interleave
59 Exiting protected mode for first time
5A Determine system board memory size
5B Relocate shadow RAM
5C Configure EMS
5D Set up wait state configuration
5E Re-test 64K RAM
5F Test shadow RAM
60 Test CMOS RAM
61 Test video
62 Test and initialize DDNIL bits
63 Test protected mode interrupt
64 Test address line A20
65 Test memory address lines
66 Test memory
67 Test extended memory
68 Test timer interrupt
69 Test real time clock (RTC)
6A Test keyboard
6B Test 80x87 math chip
6C Test RS232 serial ports
6D Test parallel ports
6E Test dual card
6F Test floppy drive controller
70 Test hard drive controller
71 Test keylock
72 Test pointing device
90 Setup RAM
91 Calculate CPU speed
92 Check configuration
93 Initialize BIOS
94 POST Bootstrap
95 Reset IC's
96 PEAK: System board POS.   NEAT/OC8291 ELEAT: Test /initialize cache RAM and controller.
97 VGA power on diagnostics and setup
98 Adapter BIOS
99 Re-initialize DDNIL bits
A0 Exception 0
A1 Exception 1
A2 Exception 2
A3 Exception 3
A4 Exception 4
A5 Exception 5
A6 Exception 6
A7 Exception 7
A8 Exception 8
A9 Exception 9
AA Exception A
AB Exception B
AC Exception C
AD Exception D
C0 System board memory failure
C1 I/O channel check activated
C2 Watchdog timer timeout
C3 Bus timer timeout

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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.

Copyright © 1988 -  by Bob Hurt. All rights reserved. Bios Central is a trademark of Bob Hurt.

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