9. Accumulator Bcontains a value in the range 10 through 150. Accumulator A cont
ID: 2249051 • Letter: 9
Question
9. Accumulator Bcontains a value in the range 10 through 150. Accumulator A contains the value 0. If the value in accumulator D is considered to be signed, does the value in accumulator D equal the value in accumulator B? 10. A byte value in the range -10 to-1 is added to a byte value in the range 50 to 128. Can the sum be considered to be signed? Can it be considered to be unsigned? through $1023. The value is stored in big-endian order. locations $1000 through S1002 into the three byte unsigned integer value at locations 11. Write a code sequence which will increment the four byte value at location $1020 12. Write a code sequence which will add the three byte unsigned integer value stored in SI100 through SI 102. The values are stored in big-endian order.Explanation / Answer
Microcontroller is not mentioned in the question, hence its assumed as MC68HC12.
9. D represents concatenated A & B accumulator registers where A is upper significance. Hence 8 bit registers A & B forms 16 bit contents of D register without any consideration to sign.
10. Yes the sum is signed and it is positive number. Yes it can be considered signed. Lets take an example : Any 8 bit number can represent 0 to 255 unsigned number but the same 8 bit number can represent -128 to +127 signed number. Condition Code register and conditional branching instruction helps to deal with signed numbers.
11. LDAA $1023 ; Load least significant byte from address
INCA ; increment by 1
STAA $1023 ; store it to same address
LDAA $1022 ; read next byte
ADCA #0 ; dummy addition to take care of previous carry if generated
STAA $1022
LDAA $1021
ADCA #0
STAA $1021
LDAA $1020
ADCA #0
STAA $1020
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