# IO/M* PIN in 8085 Microprocessor

MicrocontrollerMicroprocessor8085

In Intel 8085 microprocessor I/O and memory operation are differentiated by IO/m status signal.

IO/M stands for ‘input-output/memory’. When IO/M is logic 0, it means that the address sent out by the processor is for addressing a memory location. When IO/M` is logic 1, it means that the address sent out by the processor is for addressing an I/O port.

Fig: Pin diagram of 8085

Let us consider this following example and also the voltage level at IO/M* pin. If we consider instruction MVI E, ABH then it means that ABH will be moved or copied to the register E. And as a result the previous value of E will get over written.

Hex Codes
Mnemonic
Comment
2000
1E
MVIE, ABH
E ← ABH
2001
AB

ABH as operand

This instruction will have seven T-states as shown below.

Summary − So this instruction MVI E, ABH requires 2-Bytes, 2-Machine Cycles Opcode Fetch and Memory Read) and 7 T-States for execution as shown in the timing diagram.

Published on 03-Jan-2019 17:06:41