int 0x13 ah = 0x02 (Read)

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cod3b453

Joined: 25 Aug 2004
Posts: 618

cod3b453 12 Dec 2005, 22:57

Hi

This may sound crazy, but I've lost my working code for int 0x13 ah = 0x02 (Read) and now I can't get it to work Embarassed

I think the trouble may be in ch (cylinder #), cl (sector #), and/or dh (head #) - where do these start from 0 or 1?

Here's my rubbish code:

Code:

    @@:

        ; Reset FDD
        xor ax,ax
        mov dl,[DRIVE_ID] ; DRIVE_ID = 0x00 usually
        int 0x13
        jc @b

        ; Read Sectors
        mov ax,0x0202 ; Read | 2 Sectors
        mov bx,0x0200 ;\
        mov es,bx     ; To 0200:0000
        xor bx,bx     ;/
        mov cx,0x010F ; From Cylinder 1, sector 15 ( ??? )
        mov dh,0x00   ; Head 0 ( ??? )
        int 0x13
        jc @b

This code makes the floppy seek infintely Sad

Any help would be very appreciated.

Many Thanks,

cod3b453

12 Dec 2005, 22:57

LocoDelAssembly
Your code has a bug

Joined: 06 May 2005
Posts: 4624
Location: Argentina

LocoDelAssembly 12 Dec 2005, 23:13

See this http://www.ctyme.com/intr/rb-0607.htm

[edit] mmmm, but your code works fine, I tried this:

Code:

org 100h
    @@:

        ; Reset FDD 
        xor ax,ax 
        mov dl,[DRIVE_ID] ; DRIVE_ID = 0x00 usually 
        int 0x13 
        jc @b 

        ; Read Sectors 
        mov ax,0x0202 ; Read | 2 Sectors 
        mov bx,buffer ;\
        mov cx,0x010F ; From Cylinder 1, sector 15 ( ??? )
        mov dh,0x00   ; Head 0 ( ??? ) 
        int 0x13 
        jc @b

        int 20h

DRIVE_ID db 0

buffer:

Worked perfectly, your floppy disk and FDD are healthy?

Ralf Brown wrote:

Notes: Errors on a floppy may be due to the motor failing to spin up quickly enough; the read should be retried at least three times, resetting the disk with AH=00h between attempts

Don't retry Read/Write undefinelity [/edit]

12 Dec 2005, 23:13

cod3b453

Joined: 25 Aug 2004
Posts: 618

cod3b453 16 Dec 2005, 13:44

thanks for checking it locodelassembly!

however, i realised it was memory location error Embarassed

this code it executed in real mode hence the memory limit is 0010:0000 Rolling Eyes

i feel so stupid.

16 Dec 2005, 13:44

LocoDelAssembly
Your code has a bug

Joined: 06 May 2005
Posts: 4624
Location: Argentina

LocoDelAssembly 16 Dec 2005, 13:48

no no, if you are in real mode 0200:0000 is the address 2000h and 0010:0000 is the address 100h. Remember that in real mode the effective address is Segment*10h + Offset

16 Dec 2005, 13:48

cod3b453

Joined: 25 Aug 2004
Posts: 618

cod3b453 16 Dec 2005, 18:00

so in pmode i would put 0x08:0x2000?

16 Dec 2005, 18:00

LocoDelAssembly
Your code has a bug

Joined: 06 May 2005
Posts: 4624
Location: Argentina

LocoDelAssembly 16 Dec 2005, 18:36

In pmode the things are different, the linear address is calculated as Selector.BaseAddress + Offset, if the base address is 0, then your example will access to the address 0x2000 (supposing the Limit is setted to allow access to this address).

About pmode I can't help you very much, I'd never programmed something that works with pmode (except Windows apps which has no need to worry about this because you can always access the 4 GB). However if you need something about this with the search feature of the forum you will find something, I think

16 Dec 2005, 18:36

cod3b453

Joined: 25 Aug 2004
Posts: 618

cod3b453 16 Dec 2005, 19:17

Thanks again for your help locodelassembly!

i'll keep playing around and see what happens...hopefully, sometime in the next decade i'll have something that works Laughing

16 Dec 2005, 19:17

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