LABEL: OPCODE OPERAND
LABEL references the location of this instruction in the program, so other instructions can branch (or transfer control) to this instruction.... only a few lines of code will need to be referenced in this way.
OPCODE (short for Operation Code) is the command or instruction (ie. ADD, MOVE, JUMP)
OPERAND is the arguments (or registers or memory locations or numbers on which the command operates) but not every OPCODE requires arguments.
Here are the instructions you need to know at this time:
MOV AL, 74H ;moves 74 Hex (01110100) into the AL register
TEST AL, 74H ;performs a logical AND operation, the contents of AL register AND'ed with 74H (01110100)... sets the FLAGS... and leaves AL unchanged.
JNZ GOAWAY ;jump on non zero.... IF the zero flag is NOT set, then the program branches to the label GOAWAY and continues with the instruction at that line
JMP GOAWAY ;jump all the time.... the program branches to the label GOAWAY and continues with the instruction at that line
HLT ;halts the processor.... everything stops and the only way forward is by an interrupt or by pushing the reset button
© copyright 2002 Stephen E. Mendes, Barbados.