How to execute a 11-digit instruction using different addressing modes in Python?
Last Updated :
01 Nov, 2020
Here, we have an 11 bit instruction which has first 2 bits for representing addressing mode, next 3 bits for the opcode and the last 6 bits are for the two operands, 3 bits each.
We will execute this 11 bit Instruction using four different addressing modes:-
- Direct mode: In this mode, the addresses of two operands are specified in the instruction. We can receive the actual data directly from the memory addresses.
- Indirect mode: In this mode, the addresses mentioned in the instruction are point to the effective addresses of the operands.
- Immediate mode: In this mode, the actual data is mentioned in the instruction itself.
- Register mode: In this mode, the instruction contains the addresses of the registers which contain the actual data.
We will use the first 2 bits for representing the four different addressing modes in this way:
For direct mode- 00
For indirect mode- 01
For immediate mode- 10
For register mode- 11
Next 3 bits are for representing opcode, so we can use 8 different operations maximum. We will define 6 operations and the other two will be reserve for future in this way:
000- Do nothing
001- Addition
010- Subtraction
011- Multiplication
100-Division
101-Transfer operand2 to operand1
110-Reserve for future
111-Reserve for future
The next 3 bits are for operand1 and the last 3 bits are for operand2, so the values of operands will be ranging from 0 to 7 in immediate mode.
For the direct, indirect and register mode we need to define a memory array and a register array. As we have only 3 bits for representing the addresses so the maximum number of elements in these arrays will be 8.
memory=[2,15,40,25,7,36,64,19]
register=[17,20,43,52,None,None,None,None]
Here, the memory contains 8 data and the register contain 4 data. The concept discussed above will work in the following way:
Input: 01001000100
Here, from left to right
Mode-01- Indirect mode
Opcode-001- Addition
Operand1-000- 0
Operand2 - 100- 4
As it is the indirect mode, so these operands gives the addresses of the effective address of the data.
Means, the effective addresses are present in the memory location 0 and 4 , which are 2 and 7.
And the actual data is present in the memory location 2 and 7 which are 40 and 19.
So, the result will be the addition of 40 and 19.
Output: 59
Example:
Python
memory=[2,15,40,25,7,36,64,19]
register=[17,20,43,52,None,None,None,None]
#This function execute the instruction and print the result.
def execute(st):
mode=st[:2]
opcode=st[2:5]
operand1=st[5:8]
operand2=st[8:]
print()
print("Instruction mode:",mode)
print("Opcode:",opcode)
print("operand1:",operand1)
print("operand2:",operand2)
#For direct mode
if mode=='00':
idx1=int(operand1,2)
idx2=int(operand2,2)
if opcode=='000':
print("Do nothing")
elif opcode=='001':
print("RESULT")
print(memory[idx1]+memory[idx2])
elif opcode=='010':
print("RESULT")
print(memory[idx1]-memory[idx2])
elif opcode=='011':
print("RESULT")
print(memory[idx1]*memory[idx2])
elif opcode=='100':
print("RESULT")
print(memory[idx1]/memory[idx2])
elif opcode=='101':
print("RESULT")
print("operand1=:")
print(int(operand2,2))
else:
print("Reserve For Future")
#For indirect mode
elif mode=='01':
idx1=int(operand1,2)
idx2=int(operand2,2)
idx1=memory[idx1]
idx2=memory[idx2]
if opcode=='000':
print("Do nothing")
elif opcode=='001':
print("RESULT")
print(memory[idx1]+memory[idx2])
elif opcode=='010':
print("RESULT")
print(memory[idx1]-memory[idx2])
elif opcode=='011':
print("RESULT")
print(memory[idx1]*memory[idx2])
elif opcode=='100':
print("RESULT")
print(memory[idx1]/memory[idx2])
elif opcode=='101':
print("RESULT")
print("operand1=:")
print(int(operand2,2))
else:
print("Reserve For Future")
#For immediate mode
elif mode=='10':
idx1=int(operand1,2)
idx2=int(operand2,2)
if opcode=='000':
print("Do nothing")
elif opcode=='001':
print("RESULT")
print(idx1+idx2)
elif opcode=='010':
print("RESULT")
print(idx1-idx2)
elif opcode=='011':
print("RESULT")
print(idx1*idx2)
elif opcode=='100':
print("RESULT")
print(idx1/idx2)
elif opcode=='101':
print("RESULT")
print("operand1=:")
print(int(operand2,2))
else:
print("Reserve For Future")
#For register mode
else:
idx1=int(operand1,2)
idx2=int(operand2,2)
if idx1>3 or idx2>3:
print("Invalid")
exit()
if opcode=='000':
print("Do nothing")
elif opcode=='001':
print("RESULT")
print(register[idx1]+register[idx2])
elif opcode=='010':
print("RESULT")
print(register[idx1]-register[idx2])
elif opcode=='011':
print("RESULT")
print(register[idx1]*register[idx2])
elif opcode=='100':
print("RESULT")
print(register[idx1]/register[idx2])
elif opcode=='101':
print("RESULT")
print("operand1=:")
print(int(operand2,2))
else:
print("Reserve For Future")
#driver code
st="00001000001"
execute(st);
st="01001000100"
execute(st);
st="10001000001"
execute(st);
st="11001000001"
execute(st);
Output:
Instruction mode: 00
Opcode: 001
operand1: 000
operand2: 001
RESULT
17
Instruction mode: 01
Opcode: 001
operand1: 000
operand2: 100
RESULT
59
Instruction mode: 10
Opcode: 001
operand1: 000
operand2: 001
RESULT
1
Instruction mode: 11
Opcode: 001
operand1: 000
operand2: 001
RESULT
37
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