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Hi People,
   I seem to be having trouble with my A20 gate.  It seems to be asserted (hence allowing access to the total address bus) and I can't seem to de-assert it (for simulation purposes).

To test this I have booted into MSDOS 6.22 with dos resident and himem.sys not loaded and tried utilizing the keyboard controller,  and the fast A20 @ 0x92 to no avail.  I have also interfaced with HIMEM.SYS to control the A20 (which also fails).  My bios doesn't seem to support INT 15 A20 services (AMIBIOS 2001) and there is no option within the bios controlling the A20 gate.

My motherboard 'P4S5A' has a pentium IV processor.  In addition I have also attempted to disable the A20 with both of these methods simultaneously (just in case these multiple sources are OR'D)

From these few scraps of information,  can anyone tell me anything that I might try.

Thanks in advance
  Graham

There should also be no emm386.
Post the code you use, to deassert it(may be you are doing it incorrectly: the keyboard controller is a pain)
Try using some older dos, dos 6.22 may assert a20 when it is loaded( for it's own test purposes)