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10824 of 48,823 files

1987 February 6

  • Text / Guides and how-tos
  • Jeff Johnson, writer credits
[+] Configuration Copy text
UNPROTECT FOR JUMPMAN (IBM ENTERTAINMENT FAMILY VERS 1.00) First, make a copy of the master disk using DOS DISKCOPY program. Put the original away in a safe place (i.e. under a telephone about to ring). Load DEBUG from your DOS diskette (A>DEBUG) Put the copy of the JUMPMAN disk in drive A: From the DEBUG prompt (-), type the following: (a) -L 0 0 0 2 {loads first 2 sectors from Drive A:, Track 0, starting with Sector 0} (b) -U 236 {disassemble some code} You should see something like: 2488:0236 B80804 MOV AX,0408 2488:0239 BB0000 MOV BX,0000 2488:023C B90127 MOV CX,2701 2488:023F BA0001 MOV DX,0100 2488:0242 CD13 INT 13 2488:0244 7207 JB 024D <----make sure this sucker matches 2488:0246 B80000 MOV AX,0000 2488:0249 CD13 INT 13 2488:024B EBF9 JMP 0246 If the lines match between this and your disk, you're in luck. (c) -E 0244 EB 07 {tell the program to ignore a few things} (d) -W 0 0 0 2 {save the change} (e) -Q {exit DEBUG} Your disk is now unprotected. Enjoy! For those of you interested, listed below is an explanation of what you've just done. 2488:0236 B80804 MOV AX,0408 {verify 8 sectors} 2488:0239 BB0000 MOV BX,0000 {doesn't do anything} 2488:023C B90127 MOV CX,2701 {track #27 (39 decimal), sector 1} 2488:023F BA0001 MOV DX,0100 {drive A:, side 1} 2488:0242 CD13 INT 13 {executes the verify command} 2488:0244 7207 JB 024D {on error, continue with the pgm} 2488:0246 B80000 MOV AX,0000 {if no error, reset the drive.... 2488:0249 CD13 INT 13 execute reset, and... 2488:024B EBF9 JMP 0246 begin infinite loop to 0246} Track 39 (decimal) on the disk has a screwy format - instruction #023C above tries to find sector #1 on track 39. There is no sector #1, so on the master disk, it generates an error which is picked up by line 0244. If you've made a DISKCOPY of the disk, the copy would have a sector #1, generate no error, and continue on to the infinite loop. What the change does is tell the program to continue whether or not the error occurs. The changed line now reads: 2488:0244 EB07 JMP 024D {no matter what, jump to the pgm} Jeff Johnson 2/7/87
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