Question

The instructions that are used for reading an input port and writing an output port respectively are

(a) MOV, XCHG

(b) MOV, IN

(c) IN, MOV

(d) IN, OUT

The question was posed to me in an online interview.

Origin of the question is Instruction Set of 8086/8088 in chapter 8086/88 Instruction Set and Assembler Directives of Microprocessor

Answer 1

Right choice is (d) IN, OUT

To elaborate: The address of the input/output port may be specified directly or indirectly.

              Example for input port: IN AX, DX; This instruction reads data from a 16-bit port whose address is in DX and stores it in AX

              Example for output port: OUT 03H, AL; This sends data available in AL to a port whose address is 03H.