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Some things about the 6502 simulator "Step and Trace" function. 

When  you  initially enter you are in the "Change Registers" mode.  At
this point you can change any and all of  the  6502  registers.   When
done,  hit  ESC  and  you  will  be in the execution mode. Now you can
change and/or display memory locations, set up a break point,  execute
an instruction at a time, or run at "full" speed. 

When you boot or when you hit "R" while stopped in the execution mode,
you  will  be  in  the  Change Registers mode. Keys have the following
meanings: 


     A   = Change the Accumulator
     C   = Change the Program Counter
     ESC = Go back to the execution phase
     P   = Change the Program Status register
     S   = Change the Stack Pointer
     X   = Change the X register
     Y   = Change the Y register

When you hit any of the keys above (except ESC), you will still not be
able to change the chosen register until you hit the  space  bar.  The
contents  of  the  register  will then become high lighted and you can
change it at will.  When  through  with  a  particular  register.  Hit
<RETURN>  and the changes will be permenant.  When through, hit ESC to
exit  to  the  execution  mode  where  the  keys  have  the  following
meanings: 


C = Toggle the display of code execution (on/off)
G = GO. i.e. start code execution.
S = Toggles SUBS (???) on and off
W = Set Stop At address.
X = Wipe out current Stop At address

M = Display current memory dump start address and eight values.
    Space  bar  highlights  the contents of the first displayed memory
    location. You can change it to any legal hex  value  and  have  it
    accepted  by typing <RETURN>. Use the arrow keys to move across to
    any of the eight where you can change it. 

    A second "M" highlights the start address of the display. You  can
    change it by typing or by using either of the two horiz arrow keys
    to  move it eight addresses at a time. As before, acceptance is by
    <RETURN>.  Note that if you type in an address, the  program  will
    force the least significant digit to either 0 or 8. 















a description of the 6502 simulator's "Step and Trace" function for booting from ROM an explanation of what each key does when running step and trace function in 6502 simulator a quick reference on how to use "step and trace" function manual for Step and Trace - commands