Instruction Naming Conventions

Instruction Naming Conventions:

The mnemonics assigned to the instructions are designed to indicate the function of the instruction. The instructions fall into the following functional categories:


Data Transfer Group:

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

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