The total memory location required to feed the instruction in memory is called as instruction word size. The memory location of 8085 microprocessor can accommodate 8-bits of data. To store 16-bits data, they are stored in two consecutive memory locations (i.e. 2 Bytes).
According to the instruction word size in 8085 microprocessor, there are three types of instructions:
- 1-Byte instruction
- 2-Byte instruction
- 3-Byte instruction
1 – Byte Instructions
- They include opcode and operands in the same byte.
- Operands are internal registers and coded into the instruction.
- Instructions require one memory location to store the single byte in the memory.
Note: Instructions having the only register or register pair as the operand is 1 – Byte Instructions. Instructions in the absence of operand are also 1 – Byte Instructions.
Examples:
MOV B,C
LDAX B
NOP
HLT
2 – Byte Instructions
- 1st byte specifies opcode and 2nd byte specifies operand.
- Instructions require two memory locations to store in the memory.
Note: Instructions having the 8-bit number either as an address or data as the operand is 2 – Byte Instructions.
Examples:
MVI B, 26 H
IN 56 H
3 – Byte Instructions
- In a 3-byte instruction, the first byte specifies the opcode, and the following two bytes specify the 16-bit address.
- The 2nd byte holds the low order address.
- The 3rd-byte holds the high order address.
- Instructions require three memory locations to store the single byte in the memory.
Note: Instructions having the 16-bit number either as an address or data as the operand is 3 – Byte Instructions.
Examples:
LDA 2050 H
JMP 2085 H
