Hi all,
Just out of interest I decided to lash up the circuit I did not bother with the 470 ohm resistors tying the data lines to ground. I just connected them straight to ground. I also used an external pulse generator rather than building the oscillator circuit. Most times it was powered on it needed a reset pulse before it started to count on the address lines. With no load on the address lines the swing was from ground to +5 volts. With a 470 ohm in series with a green led connected to the address lines the swing was from 0 V to about 4.5 V The voltage across the LED was 2.0 volts so the current was (4.5 - 2.0)/470 = 5.5 mA The Z80 that I used from my junk box made by ST and had the part number Z84C00AB6. At least now we know that the circuit does work.
Les.
I've built it first with the 470 ohm resistors tying the data lines to the ground. The result is that all address lines are set to 1, giving ~3.8 volts or so to my LEDs, making them light up.
I'm giving it around 12 Hz, and I can verify that this is actually 12 Hz going into the clock pin with an oscilloscope.
I've tried to connect the address lines straight to ground like you did, with the same result. I've also tried to let them float, just to see what happens. The result is the same.
I tried to replace the CPU, perhaps it was defective. The result was the same.
I'm giving it more or less exactly 5.0 volts, but I've tried 5.1 and 4.9, slight variations.
I thought perhaps that 12 Hz was fast enough that I couldn't see them blink, this should be very unlikely on the third LED though, but I put it on my scope anyway and there is just a constant +3.8 volts to all address lines, up to A15.
What voltage do you give your CPU, and what frequency on the clock pin? I don't understand why this doesn't work.