Question

Question 1: Fill the blank cells below. Assume that X=$1000. (20 marks) Addressing mode Effective address [A] Instruction LDAA 2,X+ LDAB #SA ABA STAA 4,X LDAA (1,FFD] 00 10 01 C1 18 Address FFD FFE FFF 1000 1001 1002 1003 1004 1005 1006 38 Memory content DF EE 01 4C

HCS12

Answer 1

I have given explanation in the table itself. Please refer to that.

Instruction	Addressing Mode	Effective Address	[A]	Explanation
LDAA 2,X+	Index Mode Indexed with Auto Pre increment of index register	1000	[$1000]	This will load the accumulator with the address specified in the variable x. Since this is post increment, the accumulator will have the value [$1000] and after loading the Accumulator, x will be incremented by 2. [$1000+2 = $1002]
LDAB #$A	Extended mode	1000	NA	Inform the assembler about the place where the ensuing instruction needs to be placed. LDAB #$A will store the value of A into B. B will have the value $1000
ABA	Inherent mode	1000	[$2000]	ABA means A=A+B Add the value of A&B and store it in the Accumulator According to previous instruction A has 1000 and B has 1000. So now according to the current instruction A will have $2000
STAA 4,X	Indexed Mode Indexed with Constant offset	1006	No change [$2000]	Stores the contents of A in the given memory location. First this will add 4 to X and then copy the value of the Accumulator to the memory location x = 1002 (as per instruction 1) x = 1002 + 4 = 1006 Now 1006 will have $2000
LDAA [1, FFD]	Indexed mode 16-bit offset Indirect Indexed Addressing	FFE	10	Load contents of [1+FFD] to the accumulator [1+FFD] = FFE (refer diagram given by you) The value of FFE is 10 (ref diagram) So accumulator will have the value 10

Note: I have considered the value of each registers and variables by using the previous instruction as reference. Supoose those instruction are not series of single code snippet then you can change the value alone with the help of the explanation.