Question

Encode the following instruction

opcode: 100011

(1) identify the instruction format that will be used

(2) indicate the values of each of the fields for that format in decimal

(3) convert each of these decimal values to binary

(4) represent the entire instruction as one hexadecimal value.

subu $t3,$v1,$s2

Answer 1

There are three instruction categories: R-format, I-format, and J-format.

Given,

# opcode: 100011

# Instruction: subu $t3,$v1,$s2

** First we talk about the opcode: 100011

(1)=>  Here is the given opcode= 100011, according to this opcode the instruction format come in " I-format instruction" where the instruction format contains:

• rs: register containing base address (5 bits)
• rt: register destination/source (5 bits)
• immediate: value or offset (16 bits)

According to the given opcode the following instruction is:

Example:

lw $t0, 32($s3)

where, $t0, $s3 are registers and 32 is immediate.

(2)=> Here is the instruction format with decimal values:  

Opcode	rs	rt	immediate
35	19	8	32 (offset)

(3)=> Here is the instruction format with binary values:

Opcode	rs	rt	immediate
100011	10011	01000	0000000000100000

(4)=> Here is the entire instruction as one hexadecimal value:

Binary: 1000 1110 0110 1000 0000 0000 0010 0000

Hexa: 8 E 6 8 0 0 2 0

So, the Hexa value:

0x8E680020

** Lets we talk about the instruction format:  subu $t3,$v1,$s2

(1)=>  Here is the given Instruction: subu $t3,$v1,$s2, according to this instruction, the instruction format come in " R-format instruction" where the instruction format contains:

• Opcode= 0 (Always)
• rs: 1st register operand (source register) (5 bits)
• rt: 2nd register operand (5 bits)
• rd: register destination (5 bits)
• shamt: shift amount (0 when N/A) (5 bits)
• funct: function code (6 bits)

(2)=> Here is the instruction format with decimal values:  

Opcode	rs	rt	rd	shamt	funct
0	2	1	3	0	35

(3)=> Here is the instruction format with binary values:

Opcode	rs	rt	rd	shamt	funct
000000	00010	00001	00011	00000	100011

(4)=> Here is the entire instruction as one hexadecimal value:

Binary: 0000 0000 0100 0001 0001 1000 0010 0011

Hexa: 0 0 4 1 1 8 2 3

So, the Hexa value:

0x00411823