Finally, as most of pieces arrive, I could dive into the breadboards and wires and ICs all weekend.

Now we have the Clock, Reset, 4 Phases (Fetch 1 to 3, Execute) and 12-bit PC (Program Counter) fully operational.

Lessons learned the hard way:

-The clock generator 555 IC has very weak output. It barely can feed two TTL inputs. If I put a single 3mm round led (with a huge 4,7K resistor) to see the clock ticks, it makes all the circuit to behave erratically. That is why all projects out there uses an buffer/inverter right after the 555 output to feed all the circuit.

-Baby steps, allways. The old and good XP (eXtreme Programming) mantra is especially true when dealing with (moody) hardware. For each single piece added, turn on the circuit and see if everything still runs fine.

-TTL outputs are not suited to drive leds directly, but as i'm using big resistors (4,7k as mentioned above), the current is very small (between 0,3 and 0,8 mA, depending on the TTL output, which can vary bettween 5 and 2.7 V). Surprisingly the leds show a useful bright even with such tiny current, so I can use them without bother with transistors to drive the leds.

I never felt so happy to see a bunch of leds blinking :)

Unfortunally the 6 breadboards I ordered a long ago still didn't arrive. I will buy them on local market anyway.