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regarding CMOS of the PC

Posted on 2002-04-04
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Last Modified: 2010-04-02
HI,
   i want to write datainto the CMOS mem of the PC. How can i do that?
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Question by:ttsenis
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pagladasu earned 300 total points
ID: 6918775
You access the data in CMOS by outputting to port 70h the offset of the byte you wish to read. The value can then be read from port 71h.
This is the way your application can detect particular values of CMOS settings. To write to CMOS you have to output a value to port 71h.

for eg -

Out 70h, 4 <----- 4 is offset of current hour  
In 71h, variable <----- variable contains current hour
Out 71h, 7 <----- change current hour in CMOS to 7
Make sure that you take the precaution of disabling all interrupts before reading or writing CMOS data. Use the assembly instructions CLI and STI before and after your block of code to do the read/write from CMOS.
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Author Comment

by:ttsenis
ID: 6940299
the comment from paqladasu works but the following problem appears, on reboot the cmos checksum error appears (how do i avoid that), and by the way whats the length of cmos mem.
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by:Moondancer
ID: 6979360
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