CSC270  Homework #7

Reverse engineering

An unknown 6800 program was captured with the help of an oscilloscope and the values of some of the processor signals was recorded. They are shown in Table 1 below. All the data were captured during each period of ø2.

VMA	R/W	D7	D6	D5	D4	D3	D2	D1	D0	A5	A4	A3	A2	A1	A0
1	1	1	0	0	0	0	1	1	0	0	0	0	1	1	0
1	1	0	0	0	0	0	0	0	0	0	0	0	1	1	1
1	1	1	0	0	1	0	1	1	1	0	0	1	0	0	0
1	1	0	0	0	0	0	0	0	0	0	0	1	0	0	1
0	1	##	###	###	###	###	###	###	###	0	0	0	0	0	0
1	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0
1	1	1	1	0	0	0	1	1	0	0	0	1	0	1	0
1	1	0	0	0	0	0	0	1	1	0	0	1	0	1	1
1	1	1	1	0	1	0	1	1	1	0	0	1	1	0	0
1	1	0	0	0	0	0	0	0	1	0	0	1	1	0	1
0	1	##	###	###	###	###	###	###	###	0	0	0	0	0	1
1	0	0	0	0	0	0	0	1	1	0	0	0	0	0	1
1	1	1	1	0	1	1	1	1	0	0	0	1	1	1	0
1	1	0	0	0	0	0	0	0	0	0	0	1	1	1	1
1	1	0	0	0	0	0	0	0	0	0	0	0	0	0	0
1	1	0	0	0	0	0	0	1	1	0	0	0	0	0	1
1	1	1	1	1	0	0	1	1	1	0	1	0	0	0	0
1	1	1	1	1	1	1	1	1	1	0	1	0	0	0	1
0	1	##	###	###	###	###	###	###	###	0	0	0	0	1	1
0	1	##	###	###	###	###	###	###	###	0	0	0	0	1	0
0	1	##	###	###	###	###	###	###	###	0	0	0	0	1	0
1	0	0	0	0	0	0	0	1	1	0	0	0	0	1	0
1	1	0	0	1	0	0	0	0	0	0	1	0	0	1	0
1	1	1	1	1	1	0	0	1	0	0	1	0	0	1	1
0	1	##	###	###	###	###	###	###	###	0	1	0	1	0	0
0	1	##	###	###	###	###	###	###	###	0	0	0	1	1	0
1	1	1	0	0	0	0	1	1	0	0	0	0	1	1	0
1	1	0	0	0	0	0	0	0	0	0	0	0	1	1	1
1	1	1	0	0	1	0	1	1	1	0	0	1	0	0	0
1	1	0	0	0	0	0	0	0	0	0	0	1	0	0	1
0	1	##	###	###	###	###	###	###	###	0	0	0	0	0	0


Last Updated on 3/31/00

Analyze the data and reconstruct the original program. The "###" symbols indicate that the data were not consistent, and therefore could not be read as a 1 or a 0 with definite certainty. Give the assembly listing of the program, with documentation explaining what each instructions does.

If the program contains variables, declare them and use them in your program. For example, if you have a variable at address 0001 and your program calls for the processor to load its contents into Accumulator A, then use the following notation:

            ORG  0001
       var1 DB   ?
            ...

            LDAA var1

Also provide the answer to the following questions:

1. How long does the program take to run from the first instruction to the end of its last instruction?
2. How much longer would the program take is the direct addressing mode had been replaced by extended addressing mode in the few instructions that use this mode?