Hello everyone,
Lately I was inspired by ben eater's breadboard computer, and decided to build one myself with CMOS logic instead of TTL but today I ran into problem:

After building one of the registers using the SCL4076BE (this one is for the memory adress), I saw that it does not respond to the clock signals and the data inputs are not fed to the outputs. after some testing I realised that the clock signal is delayed and that I need to hold the clock high for about 1.5 seconds until it get signed in the register and the data is fed to the flip-flops. if I hold it for shorter time the register acts as if there was no clock pulse and keeps the outputs as they were before.

I think this is a problem of capacitance in the register input, but how can I solve it?

 

You have to hold the clock HI for 1.5 seconds?! On a part that is spec'ed to operate at up to 12 MHz (typical at Vcc = 10 V, and a minimum of 3 MHz at Vcc = 5 V)?

I'd say you are doing something wrong. Are ALL of the inputs properly driven (none of them are unconnected)?

It would sure help if you could provide a sketch of the circuit that is giving you problems.

 

Ok. thank you for pointing this out for me. I checked the register again and saw that even if I sign short clock pulses they are signed to the register SOMETIMES. By that I mean that while pressing the manual clock button about 5 times (for short amount of time), only one will be signed in the register and the inputs will be fed inside. I have an indicator led on the clock signal and it is on always when I push the button, but the register seem to ignore some of the pulses. the line data switcher works fine and there is no problem using the dip switch to change the data, all inputs are either low or high, and the clock itself work as expected. so I'm sure the problem is between the register and the clock and not somewhere else.
do you have an idea what is the problem?

 

Supply a circuit diagram and we will be in a better position to help you.

 

The problem seem to got fixed by itself, the register respondts to all the clock pulses perfectly.

thank you all anyway!

 

The problem seem to got fixed by itself, the register respondts to all the clock pulses perfectly.

thank you all anyway!

It is not likely that the problem got fixed by itself.
It is instructional to other experimenters if you document and share what was done to fix a problem.

At is what AAC is all about.

 

Ok so after I wrote that the problem got fixed by itself I saw that it came back - so I thought maybe the voltage level from the clock is too low to always count as a logical '1' pulse at the register and looked at my clock output. what I saw there is the LED that was used to show the clock pulses. So I thought: "Maybe the led 'steals' the current from the clock output?"(I know this is kinda strange because its connected in parallel from the clock output directly to ground) so I pulled out the LED from there and the register just signs all the pulses now!

Any way I'd like to know why this happend while the LED was connected in parallel to the clock output.

 

Ok so after I wrote that the problem got fixed by itself I saw that it came back - so I thought maybe the voltage level from the clock is too low to always count as a logical '1' pulse at the register and looked at my clock output. what I saw there is the LED that was used to show the clock pulses. So I thought: "Maybe the led 'steals' the current from the clock output?"(I know this is kinda strange because its connected in parallel from the clock output directly to ground) so I pulled out the LED from there and the register just signs all the pulses now!

Any way I'd like to know why this happend while the LED was connected in parallel to the clock output.

The LED will steal current from the output. Before you connect an LED to an output, you need to buffer the signal first using a logic gate such as an inverter or you can use a transistor (BJT or FET) then use that to drive the LED.

 

If you had the LED directly connected from the output to ground with no limiting resistor as shown in your attachment, than the output voltage is clamped to the forward drop voltage of the LED.
If so, it's not surprising you had problems.

 

Thank you all for helping me - I learned a lesson about LEDs today.