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Information on the meaning of POST codes for different BIOSes is needed to interpret the codes. This may be supplied with cards, but becomes dated as later BIOSes are issued; more up-to-date information may be available on manufacturers' and independent websites.
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made motherboards inexpensive components. Motherboards were rarely repaired, but replaced; the main purpose of a POST card is to determine that parts mounted on the motherboard itself, rather than plugged-in video cards, RAM, etc. are at fault.
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and other debug tools and interfaces. They are less commonly used in the 21st century for computer repair and by system integrators, but remain available. POST cards for PCs, while originally high-priced, cost from just a few
209:(usually 80 hex) during startup, some indicating a stage in the startup procedure, others identifying errors. The description for each code must be looked up in a table for the particular BIOS. For example, for the 1984
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bus, or for a parallel port. A typical card for desktop computers has a different bus interface on each edge; a card for laptop computers may have both a miniPCI and a parallel port connector (plus USB to supply power).
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POST cards provide information even when a standard display is not available, either because connecting a monitor is impractical, or because the failure occurs before the video subsystem is operational.
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Some motherboards have a built-in display to diagnose hardware problems. Most also report POST errors with audible beeps, if a PC speaker is attached. Such motherboards make POST cards less necessary.
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Modern motherboards often do not broadcast POST codes to their PCI Express slots (PCIe switches only pass on transactions after having been configured to do so by the BIOS). On such motherboards, the
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upon which the POST card relies on are all working, a POST card can be used to monitor the system's Power-On Self Test (POST), or to diagnose problems with it. The system introduced on
273:(TPM), may be the only bus where POST messages can still be seen. However LPC connectors are not standardized, with between 9 and 19 pins and both 2.54 mm and 2 mm
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When these diagnostic cards were first introduced motherboards were expensive and well worth troubleshooting and repairing. By the late twentieth century
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In addition to displaying numeric codes, many cards monitor power supply voltages, clock and oscillator signals, reset signal, and other parameters.
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BIOS POST card with connectors for the PCI (bottom), PCIe (top) and LPC (left 2 mm and right 2.54 mm) busses
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Two POST seven-segment displays ("Q_CODE1" and "Q_CODE2", lower-left), integrated on a computer motherboard
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Diagnostic cards are today mainly used by designers of motherboards and extension cards, along with
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commonly used. Therefore, an LPC POST card may have to auto-detect first the pin assignment used.
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An example of a POST diagnostic card which tests several parameters in addition to the hex codes
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POST cards are inserted into an expansion slot, and are available with connectors for the
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Another option are USB POST cards such as AMI Debug Rx, which use the
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393:"General Qcode / Q-code / Post Code table for ASUS motherboards"
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computers sends 8-bit byte codes (usually displayed as two
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that displays progress and error codes generated during
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219:8042 Keyboard Controller Failure, 105 System Error
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133:show the POST-code. Four
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45:Please help
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62:"POST card"
398:2019-07-31
378:2019-07-19
352:References
346:Debug port
314:US dollars
193:, and the
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229:Operation
211:IBM PC/AT
163:POST card
159:computing
103:July 2009
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335:See also
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175:start up
18:Postcard
249:, Mini
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199:IBM PC
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251:PCIe
239:EISA
191:BIOS
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187:CPU
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