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From: wei@hpctdls.HP.COM (Bill Ives)
Newsgroups: comp.sys.ibm.pc
Subject: Re: Drive type 20 setting
Message-ID: <2010010@hpctdls.HP.COM>
Date: 13 Apr 89 14:26:20 GMT
References: <1898@umbc3.UMBC.EDU>
Organization: Hewlett-Packard CTD, Colo. Spgs.
Lines: 59

> / hpctdls:comp.sys.ibm.pc / battle@umbc3.UMBC.EDU (Rick) /  7:52 am  Apr 11, 1989 /
> I have an IBM AT with a new Seagate ST-4038 hard drive. The
> controller is a 16 bit Western Digital.
 
> According to the documentation I have the ST-4038 is a drive
> type 20.  My IBM Advanced Diagnostic setup disk only allows
> drive types to range from 1 to 15.  How do I set the drive
> type to 20?
 

  To force the drive type to another value, you have to change
  its value in the cmos of your system.  According to my
  tech ref manual:

    CMOS Fixed Disc Type ( CMOS Address 12H )
    contains the one byte disk type you require.

    To write to the cmos you must use your AT's method of
    updating its cmos.  My ref ( which is for HP ES-12 an AT clone )
    has a function for doing this in its V_SYSTEM driver:

     Vector Address   Func Value    Definition
     12h              22h           Read and verify cmos memory

         On entry: BP = 12h
                   AH = 22h
                   BL = address of cmos byte to read.
         On exit:  AH = return status code
                   AL = byte of data from cmos
         Registers altered: ax,bp,ds

         sample code:   mov  bp,12h
                        mov  ah,22h
                        mov  bl, address_in_cmos
                        push ds       ; save ds
                        int  6fh      ; int 6fh for ex-bios
                        pop  ds       ; restore ds

     12h              24h           write to cmos memory

         On entry: BP= 12h
                   AH = 24h
                   AL = byte of data to be written to cmos
                   BL = address of byte to be written to cmos
         On exit: AH = return status code
         Registers altered: ax,bp,ds

      
     I do not know if this will work on an IBM-AT, you should probably
     check your tech ref manual first -- or you can just try it if
     your not worried about resetting up your system if it fails --
     this is risky ....
     Hope this helps some.

     - Bill Ives
       HP CTD

    #include <std-disclaimer> // These are only my opinions and
             probably are not those of HP... you know the bit.