I'm writting MCS6502 emulator, and i want to know how this processor is dealing with devices like keyboard, display, hard drive or other.
I know it's using memory mapped to device registers, but i want to know how reading from keyboard or writting to screen is accomplished by programmer.

Welcome to the forum! The MCS6500 Family Hardware Manual and Software Manual will give you a good education in the basics of how the processor deals with external devices. But this is general information. The interfaces for keyboard, display, and hard drive vary widely between all the different 6502 computers, so eventually you will need to be specific about what machine you wish to emulate. (You didn't mention.)

cheers,

Jeff

How it deals with those things will depend entirely on the I/O ICs you go through and how the keyboard, display, and other things are connected to those ICs. Their various registers are seen by the processor as if they were just memory locations though. For example, LDA $4000 might read from RAM on one computer, or read from port B of a 65c22 Versatile Interface Adapter IC on another, and from ROM on yet another computer. The processor doesn't care. And on the one that has the 65c22 VIA there, what's connected to port B might be the rows of a keyboard, the data lines of a printer port, and/or a lot of other things.

You should download and play with a copy of the Kowalski simulator to get some ideas on how you might proceed. The K-sim simulates the 6502 (or 65C02) and has an I/O "console," as well as the ability to generate regularly spaced (jiffy) IRQs. It doesn't emulate a particular machine however.

I guess the question you will have to settle is exactly what you want the finish product to do.

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Thanks for answers. Of course programming manual i've read already. What system i want to emulate? I don't care - i want user to specify where he wants to put wich device.