Answer to Question #93271 in Assembler for Umair Khan

Question

Design an ISA whose characteristics are:
1. 16 different operations
2. 12 bit address (PC, MAR etc)
3. 16 bit data registers
4. 16 bit IR

Q1. What will be the instruction size?
Q2. Opcode size?
Q3. Operand size?
Q4. Number of locations in memory?
Q5. Memory data size?

Answer 1

1. Operations:

1) Addition (ADD)

2) Substraction (SUB)

3) Carry addition (CAD)

4) Carry substraction (CSB)

5) Multiplication (MUL)

6) Division (DIV)

7) AND

8) OR

9) XOR

10) NOT

11) Load (LOD)

12) Store (STR)

13) Write (WRT)

14) Interrupt Enable (INTE)

15) Interrupt Disable (INTD)

16) Halt (HLT)

2. 1) Memory Address Register (MAR): it stores the memory address from which data will be fetched from the CPU (12-bit)

2) Program Counter (PC): it stores the address (12-bit) of the following command (it is also a register)

3. 32 16-bit data registers

4. 16-bit Instruction Register (IR): it stores the current instruction

Q1: The instruction size equal to 2 bytes (IR stores 16-bit instruction)

Q2: Opcode: 2 bytes (because the instruction size equal to 2 bytes)

Q3: Operand size: 2 bytes (the operand size is the data size)

Q4: 256 KB (128 KB - data, 128 KB - command codes)

Q5: 128 KB