!lm12
!rm76
A Correction to "Step-Trace Utility"....Bob Sander-Cederlof

"Step-Trace Utility", published in the July 1981 issue of AAL (pages 17-20), has a bug.  Three or four of you ran into the problem and called me about it, but I was never able to duplicate the problem.  Finally Bob Leedom managed to pinpoint the bug, and I found out how to fix it.

If you have used Step-Trace, you might have noticed that it sometimes will hang-up or go crazy after a relative branch instruction.  The problem is that if the 6502 was in decimal mode, the calculations are all incorrect.  This affects the branch target, and also messes up screen output.  To fix it, insert the following line:

     2095        CLD          SELECT bINARY MODE

But how did the 6502 get into decimal mode, when I wasn't ever setting it?  The contents of SAVE.P were random on initial start-up.  Sometimes the contents managed to switch on decimal mode!  Perhaps you should also insert the following two lines, to be certain of the initial status of the program you are tracing:

     1455        LDA #0       CLEAR INITIAL STATUS
     1456        STA SAVE.P

Future copies of Quarterly Disk #4 already have these two patches installed.

