CO2:Interpret the M68HC11 instruction sets Mappiag CO,PO,Domain,Kl: CO1,PO1 C03:

Question

CO2:Interpret the M68HC11 instruction sets Mappiag CO,PO,Domain,Kl: CO1,PO1 C03: Develop a firmware using 68HC11 assembly language Part A [15 marks] Q1. What are the contents of ACCA and ACCB if the following program is executed? ORG $700 LDAX #DATA LDAA 0,X ADDA 1,X BCS FKEE TAB BRA SKIP FKEE LDAB 3,X SKIP ORG $800 DATA FCC 11 22 33 44 55 66 (4 marks) 02. If the following program is executed, determine the number of BNE instruction to be executed? LDAB #10 AGAIN3 LDAA #5 AGAIN2 DECA BNE AGAIN2 DECB BNE AGAIN3 (2 marks) ASA FKEE UMP

Explanation / Answer

Q 1

ORG $700           ; It’s an assembler directive to store program in given memory location

LDAX #DATA       ; Load Index register X with the address of DATA

LDAA 0, X            ; Read first element of DATA into A register (A = 11)

ADDA 1, X           ; Add second number from DATA array to Accumulator A (A = 11 + 22 = 33 in hex)

BCS FKEE1           ; skip this as no carry generated from previous operation

TAB                       ; Transfer A to B (i.e. A = B = 33 in hex)

BRA SKIP              ; Branch to SKIP (SKIP is a label that assembler convert to address)

Hence Accumulator A = B = 33 in hex / 51 in decimal

Q 2

It’s a nested loop condition.

Internal loop causes BNE to execute 5 times as A decrements by 1 every iteration. In fifth iteration comes out of internal loop

Again external loop gets decremented by 1 and branch back to AGAIN3 if reg B not zero.

Hence AGAIN2 BNE instruction executes 5 x 10 = 50 times (45 times true and 5 times false)

AGAIN3 BNE instruction executes 10 times (9 true and 1 false)

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