An instruction is a binary pattern designed inside a microprocessor to perform a specific function. The entire group of instructions, called the instruction set, determines what functions the microprocessor can perform. These instructions can be classified into the following five functional categories: data transfer (copy) operations, arithmetic operations, logical operations, branching operations, and machine-control operations.
Data Transfer Croup
The data transfer instructions move data between registers or between memory and registers.
MOV Move
MVI Move Immediate
LDA Load Accumulator Directly from Memory STA Store Accumulator Directly in Memor
LHLD Load H & L Registers Directly from Memory SHLD Store H & L Registers Directly in Memory
An 'X' in the name of a data transfer instruction implies that it deals with a register pair (16-bits);
LXI Load Register Pair with Immediate data
LDAX Load Accumulator from Address in Register Pair STAX Store Accumulator in Address in Register Pair XCHG Exchange H & L with D & E
XTHL Exchange Top of Stack with H & L
Arithmetic Group
The arithmetic instructions add, subtract, increment, or decrement data in registers or memory.
ADD Add to Accumulator
ADI Add Immediate Data to Accumulator ADC Add to Accumulator Using Carry Flag
ACI Add Immediate data to Accumulator Using Carry SUB Subtract from Accumulator
SUI Subtract Immediate Data from Accumulator
SBB Subtract from Accumulator Using Borrow (Carry) Flag
SBI Subtract Immediate from Accumulator Using Borrow (Carry) Flag INR Increment Specified Byte by One
DCR Decrement Specified Byte by One INX Increment Register Pair by One DCX Decrement Register Pair by One
DAD Double Register Add; Add Content of Register Pair to H & L Register Pair
Logical Group
This group performs logical (Boolean) operations on data in registers and memory and on condition flags.
The logical AND, OR, and Exclusive OR instructions enable you to set specific bits in the accumulator ON or OFF.
ANA Logical AND with Accumulator
ANI Logical AND with Accumulator Using Immediate Data ORA Logical OR with Accumulator
OR Logical OR with Accumulator Using Immediate Data XRA Exclusive Logical OR with Accumulator
XRI Exclusive OR Using Immediate Data
The Compare instructions compare the content of an 8-bit value with the contents of the accumulator;
CMP Compare
CPI Compare Using Immediate Data
The rotate instructions shift the contents of the accumulator one bit position to the left or right:
RLC Rotate Accumulator Left RRC Rotate Accumulator Right RAL Rotate Left Through Carry RAR Rotate Right Through Carry
Complement and carry flag instructions:
CMA Complement Accumulator CMC Complement Carry Flag STC Set Carry Flag
Branch Group
The branching instructions alter normal sequential program flow, either unconditionally or conditionally. The unconditional branching instructions are as follows:
JMP Jump CALL Call RET Return
Conditional branching instructions examine the status of one of four condition flags to determine whether the specified branch is to be executed. The conditions that may be specified are as
follows:
NZ Not Zero (Z = 0) Z Zero (Z = 1)
NC No Carry (C = 0) C Carry (C = 1)
PO Parity Odd (P = 0) PE Parity Even (P = 1) P Plus (S = 0)
M Minus (S = 1)
Thus, the conditional branching instructions are specified as follows: Jumps Calls Returns
C CC RC (Carry)
INC CNC RNC (No Carry) JZ CZ RZ (Zero)
JNZ CNZ RNZ (Not Zero) JP CP RP (Plus)
JM CM RM (Minus)
JPE CPE RPE (Parity Even) JP0 CPO RPO (Parity Odd)
Two other instructions can affect a branch by replacing the contents or the program counter:
PCHL Move H & L to Program Counter RST Special Restart Instruction Used with Interrupts
POP Pop Two Bytes of Data off the Stack XTHL Exchange Top of Stack with H & L SPHL Move content of H & L to Stack Pointer I/0 instructions
IN Initiate Input Operation OUT Initiate Output Operation Machine Control instructions EI Enable Interrupt System
DI Disable Interrupt System HLT Halt
NOP No Operation