Write/Read stuff from CMOS Or reset the CMOS

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badc0de02

Joined: 25 Nov 2013
Posts: 216
Location: %x

badc0de02

hi, i have a qeustion how to write or read the CMOS
i know that the CMOS ports are I/O ports 70h and 71h.
but i dont know how to write to the CMOS.
need Help, im a beginner in OS Development
can some one Write a driver examnple or find a good example?
thanks in advance! Confused

23 Dec 2013, 10:49

baldr

Joined: 19 Mar 2008
Posts: 1651

baldr

badc0de02,

First link in Google Search results for "read cmos" refers to all the necessary information.

23 Dec 2013, 11:19

badc0de02

Joined: 25 Nov 2013
Posts: 216
Location: %x

badc0de02

how about a example in ASM?

23 Dec 2013, 14:20

baldr

Joined: 19 Mar 2008
Posts: 1651

baldr

Code:

; Read date and time from RTC
        org     0x100
macro cmos_read index* {
        mov     al, index
        out     0x70, al
        in      al, 0x71
}
macro cmos_read_and_convert [index*] {
        cmos_read index
        aam     16
        xchg    ah, al
        or      ax, '00'
        stosw
        inc     di
}
        mov     dx, result
        mov     di, dx
        cmos_read_and_convert 9, 8, 7; date
        cmos_read_and_convert 4, 2, 0; time
        mov     ah, 9
        int     0x21
        ret

result  db      '00-00-00 00:00:00', 13, 10, '$'

23 Dec 2013, 14:51

badc0de02

Joined: 25 Nov 2013
Posts: 216
Location: %x

badc0de02

Thanks, baldr!

23 Dec 2013, 17:18

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