From: king621@nospicedham.comcast.net   
      
   The code below is parts from a program that reads FAT16 partitions and   
   prints the root directory of the current one. Originally I could change   
   drives (partitions) and print the root directory of the next one, change   
   again and print that one.  I used a 'dir' command to print the   
   directory. Suddenly it didn't work the same.  The first time I entered   
   dir it printed the directory ok but when I changed to another drive and   
   entered dir it printed the directory of the first one printed.  That is   
   the only directory that would print regardless of which drive I changed   
   to.  I found out that the int 0x13 ah=0x42 was only being performed   
   successfully for the first time I entered dir command.  Subsequent tries   
   set the carry flag (CF) indicating a failure and the buffer at j2snd   
   (segment 0x9e) wasn't updated for the next drive - so the program   
   printed the same directory listing for every dir command.   
      
   The code below doesn't have a dir command and doesn't print a directory.   
     Every time  you hit the enter key the program executes the int13/ah42   
   sequence and prints the hex digits in the ah register if CF gets set.   
   So the first time you hit enter it prints nothing and subsequent times   
   it prints the hex digits. The hex digits are '42' - not an error   
   indication.  I checked the code carefully and found an anomaly. When the   
   line:   
      
      cmd_findfl db 'findfl',0   
      
   is commented out the problem goes away.  Then no CF gets set after   
   int13/ah=42 is performed.  What the hell?  I can't go on with arbitrary   
   things like that happening.  Pleae help.   Bill S.   
      
      
   bits 16   
   org 0x7e00   
      
   SECTION  .data   
      
   int13pkt times 16 db 0	;space for int13/ah42 packet   
   ms_invdr db 'invalid drive letter',0   
   ms_inv13 db 'an input field has more than 12 characters',0   
   ms_inv2b db 'two blank spaces is illegal',0   
   ms_hi db '   Hello World!',0   
   ms_badc db 'unrecognized command',0   
   ms_help db 'clear, copy, date, dir, drive, findbs, findfl, help, hi,   
   parts, time, txt',0   
   ms_dt_err db  '    no BIOS date/time.',0   
   ms_txcmds db '  alt-(O)pen  alt-(C)lose  alt-(S)ave  alt-save(A)s   
   alt-e(X)it',0   
   ms_f2open db '  name of file to open:',0   
   ms_f2save db '  name of file to save:',0   
   ms_fdne db '  file does not exist. Create? y/n:',0   
   cmd_clear db 'clear',0   
   cmd_copy db 'copy',0   
   cmd_date db 'date',0   
   cmd_dir db 'dir',0   
   cmd_drive db 'drive',0   
   cmd_findbs db 'findbs',0   
   cmd_findfl db 'findfl',0	;this line breaks it   
   cmd_help db 'help',0   
   cmd_hi db 'hi',0   
   cmd_parts db 'parts',0   
   cmd_time db 'time',0   
   cmd_txt db 'txt',0   
      
   kbuf   times 64 db 0   
   buf1   times 13 db 0   
   buf2   times 13 db 0   
   buf3   times 13 db 0   
   buf4   times 13 db 0   
   pbuf   times 80 db 0   
   arg2dne db 0   
   fname1 times 13 db 0   
   fname2 times 13 db 0   
   txoname times 13 db 0   
      
   scrbfc	dw 0		;byte count of screen buffer   
      
   bgfg	db 0x0f		;bg/fg=blk/wht   
   js2nd	dw 0x9e0	;segment at end of jsec2   
      
   ptdat 	times 2 dw 0	;partition data   
      
   lasdrv	db 0		;drive letter of last drive   
   curdrv	db 0x61  	;drive letter of current drive - init is 'a'   
   txoflag db 0		;   
   bign	times 2 dw 0   
   bslba1  times 2 dw 0	;32-bit sec# of bs of current drive   
   bslba2	times 2 dw 0	;a copy of bslba1   
   clstr1 dw 0   
      
   times 0x600-($-$$) db 'k'   
      
   SECTION  .text   
      
   	mov si,0			;location of this info packet in data seg.   
   	mov word[si],16			;packet size   
   	mov word[si+2],1		;# of sectors to load   
   	mov word[si+4],0		;offset  - where to load sectors   
   	mov word[si+6],js2nd		;segment - where to load sectors   
   	mov word[si+8],0		;starting absolute sector# in a quadword - mbr=0   
   	mov word[si+10],0   
   	mov word[si+12],0   
   	mov word[si+14],0   
   	mov dl,0x80			;drive number   
   	mov ah,0x42			;extended read	   
   	int 0x13   
      
   	mov ax,js2nd   
   	mov es,ax   
   	mov di,454			;point to 32-bit sector # of 1st part.   
   	mov ax,word[es:di]   
   	mov word[ptdat],ax   
   	mov ax,word[es:di+2]   
   	mov word[ptdat+2],ax   
      
   mainloop:   
   	mov ah,0   
   	int 0x16 		; wait for keyboard i/p   
   	mov di,ptdat   
   	mov si,0		;location of this info packet in data seg.   
   	mov word[si],16		;packet size   
   	mov word[si+2],32	;# of sectors to load - root dir.   
   	mov word[si+4],0	;offset  - where to load sectors   
   	mov word[si+6],js2nd	;segment - where to load sectors   
   	mov ax,word[ds:di]   
   	mov word[si+8],ax   
   	mov ax,word[ds:di+2]		   
   	mov word[si+10],ax   
   	add word[si+8],513	;points to 1st sector of root dir.   
   	adc word[si+10],0   
   	mov word[si+12],0   
   	mov word[si+14],0   
   	mov dl,0x80		;drive number   
   	mov ah,0x42		;extended read	   
   	int 0x13   
   	jnc ok   
   	mov cx,2   
   hxob:				;call with binary in ax, #digits in cx   
   	rol ax,4		;put hi hex digit on right   
   	push ax			;save rol'd ax   
   	and al,0x0f		;masks digit on right   
   	add al,'0'		;0 thru 9   
   	cmp al,'9'   
   	jbe xo3x   
   	add al,0x7		;A thru F   
   xo3x:   mov ah,0xe			   
   	int 0x10		;write to screen   
   	pop ax			;rol'd version of ax   
   	dec cx   
   	jnz hxob		;one digit per loop   
   ok:	jmp mainloop   
      
   times 0x1A00-($-$$) db 'z'	;0x1A00=13x512   
   ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;   
      
   --- SoupGate-Win32 v1.05   
    * Origin: you cannot sedate... all the things you hate (1:229/2)