SUB - MIPS instruction reference

subSubtract with overflow trap 
Subtracts $t3, or an immediate, from $t2 into $t1 and traps if the signed result overflows.
Used in The 32 registers and their namesMIPS assembly
The MIPS instruction setMIPS assembly
The bitmap display and keyboard registersMIPS assembly
Moving values aroundMIPS assembly
Variables in memory and constantsMIPS assembly
A jump tableMIPS assembly
Read two numbers and print their sumMIPS assembly
Drawing shapes on the screenMIPS assembly
A bouncing ballMIPS assembly
Flappy birdMIPS assembly
 
Forms  sub , ,   
Pseudo-instructionsThe assembler turns these into one or more real instructions.
  sub , ,   
Operands $t1 Any general-purpose register, $0 to $31, using its numeric or named spelling, such as $8 or $t0 ($zero is $0; $ra is $31). 
$t2 A general-purpose register. It may be the same register as $t1. 
$t3 A general-purpose register. It may be the same register as $t1. 
imm An immediate value: a signed 16-bit value (-32768 to 32767) or a 32-bit value (-2147483648 to 4294967295). The assembler chooses a supported encoding for the value and other operands; a pseudoinstruction may expand into several instructions. 
Raises an overflow exception if the true result does not fit in 32 bits. Use 'subu' when overflow should be silently ignored.
 # Initialize both inputs, then execute sub with initialized inputs. Inspect $t2: 4.
li $t0, 7
li $t1, 3
sub $t2, $t0, $t1