Produce an execution history for the code below ORG 0080 Sum

Produce an execution history for the code below:

ORG $0080

Sum: DS.B 1

ORG $FC00

Start: lda Ax

sub #$AB

sta Sum

Done: bra Done

Ax: DC.B $12

ORG $FFFE

DC.W Start

Solution

This is the code for assembly language programming.

ORG The ORG pseudo-op, for ORiGin, specifies the location for the assembler to deposit the machine code (or object code). In assembly language programming, all code should be preceded by the following ORG command.An assembler program typically has its own set of commands, called pseudooperations or pseudo-ops, used to direct the assembly process. These pseudo-ops seem like real instructions, but they are interpreted as control information to the assembler rather than assembled into machine code.

DS.B defines storage bytes.

dc.w defines a constant word.

lda Ax loads the contents of Ax register into the accumulator.

STA copies the data byte from the accumulator in the memory location specified .

bra is a jump instruction.

dc.b $12 initializes a three byte constant with the data.

ORG $0080 =0080

DS.B 1 =0080+0001

ORG $FC00

LDA AX load the contents defined by ax into accumulator

SUB #$AB

sta SUM copies the contents of accumulator to location defined by sum i,e 0081

bra Done jump to done

DC.B $12 initializes three byte constant

ORG $FFFE system reset

DC.W Start it declares a constant word start

In the above program sum,start,done,ax are symbols and a seperate symbol table needs to be prepared with their specific memory locations,