All posts by MalibuJack

6502 emulated in microcontroller (Part 5) IT LIVES!

I found the 74hc299 shift register was giving me fits, so I removed it for now and wired the data bus temporarily directly to the arduino to work through reading and writing to ram.  I started by writing a repeating but easily distinguishable pattern to the ram to make sure it can write to all the ram and read it back.  64kb in 2 chips of 32kb.
I can come back later and add the shift register back.
I then patched the 6502 emulator code to read and write to the RAM. There seems to be some slower performance that I am tracking down.  I hope that the shift register performance isnt too slow.  I did notice that splitting the address into two bytes by doing bitshift seems slow.  And I haven’t started figuring out what to use for rom or sdcard, and memory mapping.

It lives! Running EHBasic 2.22 rom.

I have to collect up the links for the EHBasic project and the Arduino 6502 project I based my modifications on.  I do plan on cleaning up the code and posting it.

6502 emulated in microcontroller (Part 4)

One step closer.  I have both the address bus (orange wires) and data bus (green wires) working and reading.  I am able to select the memory address and bank (chip select) and the data bus latches and displays the bits stored.  I still have to work through the details of using the universal shift register and timing the memory writes with it so it can read and write bytes to the bus. 

A very photogenic breadboard!

Once I have that working I can patch the 6502 emulator to use the external ram instead of the microcontroller ram.  Turns out the method I used to select the ram, is similar to how you would do bank switching on an Apple II.  Once I have a method to dynamically map memory, I have to decide where the zero page and registers will reside,  if I use microcontroller ram,  I can’t spy on those items, but it may prove faster.  I haven’t even thought about video display or physical I/O