Question

(Computer Assembly Language)

54. In a pure load store architecture, no instructions other than the load and store instructions are allowed to directly access memory. page: 275

 Short Answer 

55. Given the instruction set for MARIE 

Write the assembly language equivalent for the machine instruction: 0011 000000000101 Page: 236 

56. Given the instruction set for MARIE 

Write the assembly language equivalent for the machine instruction: 1011 000000001111 Page: 236 

57 Given the instruction set for MARIE 

Wite the assembly language equivalent for the machine instruction: 1000 100000000 Page: 236

Answer 1

The instruction set for MARIE is given.

In MARIE, each instruction is of 16 bits in which first 4 bits represent the opcode and last 12 bits are used for representing the address.

For example-

In instruction 1000010101010110

1000 represents opcode

01010101010110 represents address

From the table given if we convert instruction opcode from hexadecimal to binary-

Instruction opcode	Instruction
0000	JnS X
0001	Load X
0010	Store X
0011	Add X
0100	Subt X
0101	Input
0110	Output
0111	Halt
1000	Skipcond
1001	Jump X
1010	Clear
1011	AddI X
1100	JumpI X

Now coming on to the questions:

Q.55 Write the assembly language equivalent for the machine instruction:

0011 000000000101

0011 represents opcode

000000000101 represents address

From our table opcode 0011 represents the instruction Add X

that means Add the value present at address 000000000101 to the value present in the accumulator and store the result in the accumulator.

Q.56 Write the assembly language equivalent for the machine instruction:

1011 000000001111

1011 represents opcode

000000001111 represents address

From our table opcode 1011 represents AddI X

that means Add indirect that means use value present at address 000000001111 as the actual address of the operand and fetch operand by going to that address and then add the value of operand to the value present in the accumulator and store the result in the accumulator.

Q.57 Write the assembly language equivalent for the machine instruction:

1000 100000000000

1000 represents opcode

100000000000 represents address

From our table 1000 represents Skipcond

Now we will try to understand what this Skipcond is doing-

Skipcond is skipping next instruction if AC is negative, positive or zero

Now number bits from 1 to 16 starting from the last in the instruction.

Tenth and eleventh bit of instruction are used to determine the skipping condition.

if Bits 11 and 10 are 00 then this translates to skip the next instruction if AC is negative.

if Bits 11 and 10 are 01 then this translates to skip the next instruction if AC is zero.

if Bits 11 and 10 are 10 then this translates to skip the next instruction if AC is positive.

In our case they are 10 then our assembly language equivalent is:

Skip the next instruction if AC is positive.