80386 Programmer's Reference Manual -- Opcode LODS
LODS/LODSB/LODSW/LODSD -- Load String Operand
IF AddressSize = 16 THEN use SI for source-index ELSE (* AddressSize = 32 *) use ESI for source-index; FI; IF byte type of instruction THEN AL := [source-index]; (* byte load *) IF DF = 0 THEN IncDec := 1 ELSE IncDec := -1; FI; ELSE IF OperandSize = 16 THEN AX := [source-index]; (* word load *) IF DF = 0 THEN IncDec := 2 ELSE IncDec := -2; FI; ELSE (* OperandSize = 32 *) EAX := [source-index]; (* dword load *) IF DF = 0 THEN IncDec := 4 ELSE IncDec := -4; FI; FI; FI; source-index := source-index + IncDec
DescriptionLODS loads the AL, AX, or EAX register with the memory byte, word, or doubleword at the location pointed to by the source-index register. After the transfer is made, the source-index register is automatically advanced. If the direction flag is 0 (CLD was executed), the source index increments; if the direction flag is 1 (STD was executed), it decrements. The increment or decrement is 1 if a byte is loaded, 2 if a word is loaded, or 4 if a doubleword is loaded.
If the address-size attribute for this instruction is 16 bits, SI is used for the source-index register; otherwise the address-size attribute is 32 bits, and the ESI register is used. The address of the source data is determined solely by the contents of ESI/SI. Load the correct index value into SI before executing the LODS instruction. LODSB, LODSW, LODSD are synonyms for the byte, word, and doubleword LODS instructions.
Protected Mode Exceptions#GP(0) for an illegal memory operand effective address in the CS, DS, ES, FS, or GS segments; #SS(0) for an illegal address in the SS segment; #PF(fault-code) for a page fault
Real Address Mode ExceptionsInterrupt 13 if any part of the operand would lie outside of the effective address space from 0 to 0FFFFH
Virtual 8086 Mode ExceptionsSame exceptions as in Real Address Mode; #PF(fault-code) for a page fault