Lec3: instruction formats

3.1 Instruction Formats
Operands specify the value an instruction is to operate on, and where the result is to be stored. Instruction sets are classified by the number of operands used. An instruction may have no, one, two, or three operands.Based on the no. of operands in the instruction, we get four instruction formats :
1- Standard format:
2- Two address:
3- Three address:
4-Zero address: these instructions have field only, the operation field.
3.2 Instruction Length
instruction length is the number of bits or bytes which defines an instruction. This can be done simply by specifying how many bits in each field.The length of opcode field is Inferred from the No. of instruction supported by the processor to the form 2n , n will be the No. of bits for (opcode

Example :If the Cpu can do 64 instruction , then the no. of bits in the opcode field will be :64 ? 26 ? n=6
? the no. of bits =6
For a computer supports 16 instructions, The no. of bits = ---------
A computer with 20 instructions have------- bits in address field