fetching and executing instruction?

Yes, I guess so, but that's only a very broad description.

What are you trying to achieve? Do you want to design your own CPU?

If so, you should study the architectures of existing small processors such as the PIC, AVR, 8051, etc to learn exactly what they do.

 

No, you are not even close.
Very few ALU can directly access memory, they use registers.
Somewhere needs address bus setup.
The ALU is the arithmetic unit and is not involved in all instructions.
So, as I said not even close.
As I said when you posted before, this can not be described on a forum; it needs a book and very careful reading. And also needs a selection of which architecture you are after - there are several.

This should be posted on a different forum, unless you need design help with the implementation of a specific bit and have a circuit so far.

 

Have you even programmed a MC?

As far as read/write IO port:
As I said before, different architectures and implementations handle this differently, some map ports to memory, some map ports to registers, some map ports to registers and the registers into special memory addresses. Some have special IO instructions, some use normal load/store instructions to access IO ports.
So again, this question is not suitable for asking on a forum.
In general, when you apply a high signal to a pin of a port and the software uses the appropriate instructions to retrieve the status of the port, the bit representing that port/pin will contain a '1'. If a low signal is applied then it will contain a '0'.
Ports also behave differently, some are always read/write/enabled, some need to be enabled and set for read or write or any combination.
Furthermore ports can be digital or analogue inputs/outputs. Analogue ports normally have AD/DA converters so they are presented digitally to the processor..

I think you should start with a course in programming micro controllers as a lot of it will be explained on such a course. Once you fully understand how to program them, you have a much better chance of understanding the underlying electronics. And note there is a different forum for programming.

 

I/O ports are just like memory locations - they are addressed at specific addresses. The hardware detects a read or write access to the particular address, and either provides data onto the data bus (for a read), or latches data from the data bus (for a write).

Some architectures map ports into the standard data memory space, and some have a separate space that must be accessed by different instructions. The AVR can do both, but that's unusual.

Edit: I agree with shumifan. If you don't know the answers to these questions, you aren't even close to being able to design your own. Start by studying some existing architectures and learning to program them.

 

@Kris: snap

 

vead, I don't understand what you're trying to do. I think I remember a while ago you said you wanted to design a processor core. Is that what you want to do?

You seem to have the general idea of how to read I/O ports, and how the CPU/MCU core executes instructions.

You didn't ask any question in your last post, and you haven't responded to shumifan50's and my comment that you should be learning about microprocessor architectures.

Read some microprocessor and microcontroller data sheets from manufacturers like Intel, Atmel, Microchip, NXP, ON Semiconductor / Motorola, Renesas / Hitachi, Texas Instruments, Freescale, STMicroelectronics, Infineon, etc and learn how they work.

If that's too advanced, start with some general books on MPU/MCU architecture. Search for microcontroller on amazon.com and buy some books or ebooks.

 

And YOU don't answer questions:

Can you and have you programmed a micro controller?

To try and build a solution to a problem you don't understand is doomed to failure, so you have to be able to program a MC proficiently.

This is my last comment as you don't do your bit.