| Code | Mnemonic | Description |
|---|---|---|
| E4 ib | IN AL, imm8 | Input byte from imm8 I/O port address into AL |
| E5 ib | IN AX, imm8 | Input byte from imm8 I/O port address into AX |
| E5 ib | IN EAX, imm8 | Input byte from imm8 I/O port address into EAX |
| EC | IN AL, DX | Input byte from I/O port in DX into AL |
| ED | IN AX, DX | Input word from I/O port in DX into AX |
| ED | IN EAX, DX | Input doubleword from I/O port in DX into EAX |
Copies the value from the I/O port specified with the second operand (source operand) to the destination operand (first operand). The source operand can be a byte-immediate or the DX register; the destination operand can be register AL, AX, or EAX, depending on the size of the port being accessed (8, 16, or 32 bits, respectively). Using the DX register as a source operand allows I/O port addresses from 0 to 65,535 to be accessed; using a byte immediate allows I/O port addresses 0 to 255 to be accessed.
When accessing an 8-bit I/O port, the opcode determines the port size; when accessing a 16- and 32-bit I/O port, the operand-size attribute determines the port size.
At the machine code level, I/O instructions are shorter when accessing 8-bit I/O ports. Here, the upper eight bits of the port address will be 0.
This instruction is only useful for accessing I/O ports located in the processor's I/O address space. See Chapter 9, Input/Output, in the Intel Architecture Software Developer's Manual, Vo l u me 1 , for more information on accessing I/O ports in the I/O address space.
| Operands | Bytes | Clocks | |
|---|---|---|---|
| al, imm8 | 2 | 7 | NP |
| ax, imm8 | 2 | 7 | NP |
| eax, imm8 | 2 | 7 | NP |
| al, dx | 1 | 7 | NP |
| ax, dx | 1 | 7 | NP |
| eax, dx | 1 | 7 | NP |
| Operands | Bytes | Clocks | |
|---|---|---|---|
| acc, imm | 2 | 4/21/19 | NP |
| acc, dx | 1 | 4/21/19 | NP |
Cycles for: CPL <= IOPL / CPL > IOPL / V86
| ID | unaffected | DF | unaffected |
|---|---|---|---|
| VIP | unaffected | IF | unaffected |
| VIF | unaffected | TF | unaffected |
| AC | unaffected | SF | unaffected |
| VM | unaffected | ZF | unaffected |
| RF | unaffected | AF | unaffected |
| NT | unaffected | PF | unaffected |
| IOPL | unaffected | CF | unaffected |
| OF | unaffected |
