Instruction Set Classification
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.
1 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 Memory
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
2 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
3 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
4 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
INC CNC RNC (No Carry)
JNZ CNZ RNZ (Not Zero)
JM CM RM (Minus)
JP0 CPO RPO (Parity Odd)
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
5 Stack Instructions
The following instructions affect the Stack and/or Stack Pointer
PUSH Push Two bytes of Data onto the Stack
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
6 I/0 instructions
IN Initiate Input Operation
OUT Initiate Output Operation
7 Machine Control instructions
EI Enable Interrupt System
DI Disable Interrupt System
HLT Halt
NOP No Operation
