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oldlinux-files/docs/interrupts/int-html/rb-2271.htm
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<TITLE>Int 1A/AH=00h
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Int 1A/AH=00h - TIME - GET SYSTEM TIME -
AH = 00h
Return: CX:DX = number of clock ticks since midnight
AL = midnight flag, nonzero if midnight passed since time last read
Notes: there are approximately 18.2 clock ticks per second, 1800B0h per 24 hrs
(except on Tandy 2000, where the clock runs at 20 ticks per second)
IBM and many clone BIOSes set the flag for AL rather than incrementing
it, leading to loss of a day if two consecutive midnights pass
without a request for the time (e.g. if the system is on but idle)
since the midnight flag is cleared, if an application calls this
function after midnight before DOS does, DOS will not receive the
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<h2>Int 1A/AH=00h
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<h3><font color=#C00040>TIME - GET SYSTEM TIME</font></h3>
<PRE>
AH = 00h<br>
<p><b>Return:</b><br>CX:DX = number of clock ticks since midnight
AL = midnight flag, nonzero if midnight passed since time last read
</PRE>
<p><b>Notes:</b>
There are approximately 18.2 clock ticks per second, 1800B0h per 24 hrs
(except on Tandy 2000, where the clock runs at 20 ticks per second).
IBM and many clone BIOSes set the flag for AL rather than incrementing
it, leading to loss of a day if two consecutive midnights pass
without a request for the time (e.g. if the system is on but idle).
Since the midnight flag is cleared, if an application calls this
function after midnight before DOS does, DOS will not receive the
midnight flag and will fail to advance the date.
Modern releases of MS-DOS/PC DOS (5.0+???) assume that AL is a day
rollover counter rather than a flag, as expected by older releases.
DOS 5 - 7.10 (Windows 98 SE) provide an undocumented CONFIG.SYS
SWITCHES=/T option to force the old behaviour of the day advancing
code, that is using a flag instead of a counter..
DR DOS 3.31 - DR-DOS 7.03 handle AL as a flag.
<p><b>See Also:</b>
<a href="rb-2272.htm" tppabs="http://www.ctyme.com/intr/rb-2272.htm">AH=01h</a> - <a href="rb-2273.htm" tppabs="http://www.ctyme.com/intr/rb-2273.htm">AH=02h</a> - <a href="rb-2703.htm" tppabs="http://www.ctyme.com/intr/rb-2703.htm">INT 21/AH=2Ch</a> - <a href="rb-6356.htm" tppabs="http://www.ctyme.com/intr/rb-6356.htm">INT 55"Tandy
<p><b>See Also:</b>
<a href="rb-7060.htm" tppabs="http://www.ctyme.com/intr/rb-7060.htm">INT 62/AX=0099h</a> - MEM 0040h:006Ch - MEM 0040h:0070h
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Bios</a>
- <a href="int-1a-1.htm" tppabs="http://www.ctyme.com/intr/int-1A.htm">
Int 1Ah</a>
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