Hardware Reference
In-Depth Information
Systems that use UEFI firmware also perform diagnostics tests, but depending upon the
specific firmware in use, error messages may be stored in event logs and beep codes may
be used for some errors.
How Errors Are Displayed
The POST tests normally provide three types of output messages: audio codes, onscreen
text messages, and hexadecimal numeric codes that are sent to an I/O port address.
POST errors can be displayed in the following three ways:
•
Beep codes
—Heard through the speaker attached to the motherboard. Note that some
recent systems do not include a speaker.
•
POST checkpoint codes
—HexadecimalcheckpointcodessenttoanI/Oportaddress.
A special card plugged into either an Industry Standard Architecture (ISA) or a Peri-
pheral Component Interconnecct (PCI) card slot is required to view these codes.
•
Onscreen messages
—Error messages displayed onscreen after the video adapter is
initialized.
SystemsthatuseUEFIfirmwaremightusebeepandcheckpointcodes,butalsostoreerror
messages in event logs.
BIOS POST Beep Codes
Beepcodesareusedforfatalerrorsonly,whichareerrorsthatoccursoearlyintheprocess
that the video card and other devices are not yet functional. Because no display is avail-
able, these codes take the form of a series of beeps that identify the faulty component.
When your computer is functioning normally, you should hear one short beep when the
system starts up at the completion of the POST, although some systems (such as Com-
paq's)beeptwiceattheendofanormalPOST.Ifaproblemisdetected,adifferentnumber
of beeps sound, sometimes in a combination of short and long tones. Some implementa-
tions of UEFI firmware also use POST codes to report errors.
BIOS POST Checkpoint Codes
POST checkpoint codes are hexadecimal numeric codes written by POST routines to I/O
port address 80h as each major step is begun. These are often simply called POST
codes
.
These POST codes can only be read by a special adapter card plugged into one of the sys-
tem slots. These cards originally were designed for system manufacturers to use for burn-
in testing of the motherboard. Several companies make these cards available to techni-
cians. Micro 2000, JDR Microdevices, eSupport, Ultra-X, and Trinitech (search for Omni
Analyzer) are just a few manufacturers that market these POST cards.
