The following are some assembly language instructions of a hypothetical CPU. The

Question

The following are some assembly language instructions of a hypothetical CPU. The instructions are written to find the remainder when 16 is divided by 7 and store the remainder in a memory location

location assembly instruction

0 load 16

1 sub 7

2 bge 1

3 store 4

4 (unknown)

The operands of the above instructions are given in decimal.

(i) Translate the first four assembly instructions (at locations 0 to 3) into 8-bit machine language instructions (3 bits for operation code and 5 bits for operand) using the following table. Ignore the last column at this moment.

binary

operation

code

assembly

language

operation

code

For example, the assembly instruction at location 3 (store 4) is translated to "000 00100" since "store" corresponds to 000 and 410 = 001002 .

(ii) This part is difficult. Upon the reset of the CPU, the first instruction to execute is at location 0. Then the CPU executes the instructions one by one from the top to the bottom unless changed by the "bge" instruction. The machine has a register called the accumulator A which can be used to store a number. Now you need to trace the execution of the above assembly instructions.

• What is wrong with the above instructions?

• Suggest some changes in the assembly instructions that make the code work as intended.

(d) Show your working steps in performing the following conversions:

(i) Convert 0101 10012 to decimal.

(ii) Convert 4E16 to decimal.

(iii) Convert 1100 00112 to hexadecimal.

binary

operation

code

assembly

language

operation

code

operand (5 bits) meaning 100 load x load the value x into the accumulator 101 sub x
subtract the value x from the accumulator A (i.e., A - x) and store result in A. 110 add x add the value x to the accumulator A (i.e., A + x) and store result in A. 111 bge x branch to location x if the content of the accumulator A is greater than or equal to zero. In other words, if A >= 0, the next instruction to execute is at location x. Normally the next instruction's location is one larger than the current memory location. 000 store x store the content of the accumulator to location x

Explanation / Answer

i) machine code

100 10000

101 00111

111 00001

000 00100

iii)

a) Convert 0101 10012 to decimal.

89

b) Convert 4E16 to decimal.

You enter the number: 4.e16 in Hexadecimal number system and want to translate it into Decimal.
To do this, at first translate it to decimal here so :

4.e16 = 4?160+14?16-1 = 4+0.875 = 4.87510

Happened: 4.87510



Result of converting:
4.e16 = 4.87510

c) Convert 1100 00112 to hexadecimal

D3

1100 is D in Hexadecimal

0011 is 3 in Hexadecimal

Hence result D3

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