Question

Explain the different types of instruction in 8085

Answer 1

The instruction set of the 8085 microprocessor as mentioned before consists of 74 instructions with 246 different bit patterns and all these instructions can be broadly classified into five functional groups depending upon the operations that they can perform. These functional groups are: data transfer (or copy) operations; arithmetic operations; logic operations; branchingoperations; and machine-control operations.

Let us see the operations that the various instructions of each of these functional groups are capable of performing:

(i) Data transfer (or copy) operations: data transfer is more of a misnomer for such instructions since these instructions copy data (and not transfer them) from one location called the source to another location called the destination without affecting the contents of the source location. Data transfer operations can further be classified into five different types. They are:

(a) Transfer of data between registers: example is the instruction MOV B,C which copies data from register C into register B.

(b) Placing of specific data byte into a register or a memory location: example is the instruction MVI B, 67H (or MVI M, 4FH) which places the data byte 67H (or the data byte 4FH) into the register B (or the memory location M whose address is contained in the register pair HL).

(c) Transfer of data between a memory location and a register: example is the instruction LDA 2005H which copies data from a memory location having the address 2005H into the accumulator.

(d) Transfer of data between and I/O device and the accumulator: example is the instruction IN 4BH which copies data from an input device having port address 4BH into the accumulator.

(e) Transfer of data between a register pair and the stack: example is the instruction PUSH B which places the two data bytes from register pair BC into the user defined memory locations called the stack.