A20 Line: Difference between revisions
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If there is an error, the CF will be set, and the error code will be in AH. On success, the CF is clear, and AH==0. Specifically, AH==0x86 means the function is not supported, and you will have to use another method. |
If there is an error, the CF will be set, and the error code will be in AH. On success, the CF is clear, and AH==0. Specifically, AH==0x86 means the function is not supported, and you will have to use another method. |
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===Recommended Method=== |
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Because there are several different methods that may or may not be supported, and because some of them cause problems on some computers; the recommended method is to try all of them until one works in the "order of least risk". Essentially: |
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* Test if A20 is already enabled - if it is you don't need to do anything at all |
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* Try the BIOS function. Ignore the returned status. |
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* Test if A20 is enabled (to see if the BIOS function actually worked or not) |
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* Try the keyboard controller method. |
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* Test if A20 is enabled in a loop with a time-out (as the keyboard controller method may work slowly) |
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* Try the Fast A20 method last |
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* Test if A20 is enabled in a loop with a time-out (as the fast A20 method may work slowly) |
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* If none of the above worked, give up |
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==See Also== |
==See Also== |
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