Author Topic: POST Cards  (Read 781 times)

La.kl

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POST Cards
« on: May 06, 2013, 12:27:58 PM »
A POST card is a diagnostic device that plugs into the system’s expansion slot
and tests the operation of the system as it boots up. These cards can be as
simple as interrupt and direct memory access (DMA) channel monitors, or
as complex as full-fledged ROM BIOS diagnostic packages that carry out
extensive tests on the system.
POST cards are normally used when the system appears to be dead, or when
the system cannot read from a floppy or hard drive. The firmware tests on
the card replace the normal BIOS functions and send the system into a set of
tests. The value of the card lies in the fact that the tests can be carried out
without the system resorting to software diagnostics located on the hard disk
or in a floppy drive.
The POST routines located in most BIOS chips report two types of errors—
fatal and nonfatal. If the POST encounters a fatal error, it stops the system.
The error code posted on the indicator corresponds to the defective operation.
If the POST card encounters a nonfatal error, however, it notes the error and
continues through the initialization routine to activate as many additional
system resources as possible. When these types of errors are encountered,
the POST card must be observed carefully because the error code on its indicator
must be coordinated with the timing of the error message or beep code
produced by the BIOS routines.
Simple POST cards come with a set of light-emitting diodes (LEDs) on
them that produce coded error signals when a problem is encountered.
Other cards produce beep codes and seven-segment LED readouts of the
error code. Figure 3.5 depicts a typical XT/AT-compatible POST card.
IOW
IOROSC
HI TRL LO
CLK
PROBE
MEM
RST
POST
DISPLAY ALE
+12 -12 -5 +5
Figure 3.5 A typical POST card.
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