|Opcode||Instruction||Op/En||64-bit Mode||Compat/Leg Mode||Description|
|FD||STD||NP||Valid||Valid||Set DF flag.|
|Op/En||Operand 1||Operand 2||Operand 3||Operand 4|
Sets the DF flag in the EFLAGS register. When the DF flag is set to 1, string operations decrement the index regis-ters (ESI and/or EDI). Operation is the same in all modes.
DF ← 1;
The DF flag is set. The CF, OF, ZF, SF, AF, and PF flags are unaffected.
If the LOCK prefix is used.