I found a tutorial with a schematic where you can buy a PCB for an old computer with a 6502 microprocessor.
I want to do this on my own with my own PCB (but I test the circuit on my breadboard first) and I have some questions for a better understanding of the design and this old technology (which is quite interesting).
How does the program flow work? As I understand it, I will write the program into the
28C256EEPROM. The EEPROM is read-only (because of
WEhigh) and so the EEPROM will output the program data which is stored in the address range of
0xFFFF. The address bus represents the program counter and so when the program counter increases the address increases too?
Why is the NAND
U4Cconnected with the main clock? If I understand it right, the SRAM of the microprocessor is mapped in the memory region from
a15is connected with the ´CS`. But what is the reason to connect the clock with the NAND?
The memory space
0xC00Fis reserved for the I/O. So the I/O is "mapped in the same region as the SRAM" and when I write to this specific address, I will write into the SRAM and the I/O controller. Is this correct?
How does this microprocessor handle an interrupt? In my understanding, the microprocessor will change the address on the bus to
0xFFFEwhen an event on
IRQoccurs. So I have to place my interrupt code at this specific address in the EEPROM. Is that correct?
It seems that I need an EEPROM programming device to write the EEPROM. Do I have to use some kind of high voltage programming or can I use a microcontroller to write this EEPROM? Otherwise, I have to buy an EEPROM programming device.