OR

This instruction performs a bitwise OR operation between the destination operand and the source operand (destination OR source). The result is stored in the destination operand. The source operand is not modified.

The flags are modified as follows:

• CF=0.
• If the result is zero, then ZF=1. Otherwise, ZF=0.
• If the most significant bit of the result is 1, then SF=1. Otherwise, SF=0.
• OF=0.

Usage

OR dest, source

The valid combinations for dest and source are:

• Register, register
• Register, memory address
• Register, immediate
• Memory address, register
• Memory address, immediate

(See operand types)

Encoding

• REGISTER to register
  1000010w, 00RRRrrr
• Memory (direct) to register
  1000010w, 01000rrr, addr-low, addr-high
• Memory (indirect) to register
  1000010w, 01010rrr
• Memory (indirect with offset) to register
  1000010w, 01100rrr, disp-low, disp-high
• Immediate to register
  1000010w, 01001rrr, data-low, data-high
• Register to memory (direct)
  1000010w, 11000rrr, addr-low, addr-high
• Register to memory (indirect)
  1000010w, 11010rrr
• Register to memory (indirect with offset)
  1000010w, 11100rrr, disp-low, disp-high
• Immediate to memory (direct)
  1000010w, 11001000, addr-low, addr-high, data-low, data-high
• Immediate to memory (indirect)
  1000010w, 11011000, data-low, data-high
• Immediate to memory (indirect with offset)
  1000010w, 11101000, disp-low, disp-high, data-low, data-high

Where w is the operand size bit. w=0 indicates 8-bit operands, and w=1 indicates 16-bit operands. When w=0, data-high is omitted (the instruction length is one byte shorter).

rrr or RRR encodes a register according to the following table:

rrr	w=0	w=1
000	AL	AX
001	CL	CX
010	DL	DX
011	BL	BX
100	AH	SP
101	CH	--
110	DH	--
111	BH	--