6502 Computer Adventures: Part 2

 

Previously I connected up the 6502, now it was time to get the CPU to actually do something so I connected some LEDs to a couple of the address bus (pins 9- 13). I powered both circuits using a couple of AA batteries, success the LEDs started to blink randomly. 

W65C02 Pinout

Enough of the randomness I actually wanted the CPU to do something.  I hardwired the data bus so the CPU would be forced to run the same instruction over and over,  the NOP or No operation instruction was a good choice.   This does nothing for 2 clock cycles, usually used to time a delay or fill patches in a program.

I connected 16 LEDs to the address bus so I could monitor what it was doing.   The NOP instruction equates to EA in Hex or 11101010 in Binary. I hardwired the data bus (pins 26 - 33) starting at pin 26, I connected them via 1K resistors like this.

Pin	Data Bus	Connection
26	D7	+5v (1)
27	D6	+5v (1)
28	D5	+5v (1)
29	D4	0V (0)
30	D3	+5v (1)
31	D2	0V (0)
32	D1	+5v (1)
33	D0	0V (0)

Updated breadboard with the NOP / 11101010 hardwired to the 8 data pins

So I had basically made some blinkenlights, exciting times.  Watching the LEDs connected to the address bus count in a binary was quite therapeutic. 

Arduino Mega monitoring the address and data buses

In the first part of Ben Eater's 6502 videos he connected up a Arduino Mega to the address and data buses and wrote a little Arduino sketch to monitor these.