Boolean Logic Sequencer Error

[Xeys42]

I made a quick patch demonstrating the following anomaly. If you look at the attached images the first one shows the And operator working as it should, i.e. the sequencer doesn't run, however, when I select Nor and Xnor the sequencer runs. This shouldn't happen as A is on and B is off which defies the logic, and yes I have pressed the stop button before changing the modes. I'm wondering if this is a bug. Maybe it's something to do with the LFO However, changing the rate doesn't change anything.

and operator

and.png (1.13 MiB) Viewed 264 times

nor operator

nor.png (1.1 MiB) Viewed 264 times

xnor operator

xnor.png (1.09 MiB) Viewed 264 times

[ColinP]

This is the expected behaviour.

One of the inputs is disconnected therefore always zero, let's say it is the B input that's disconnected
so B = 0

Looking at the truth table for NOR

A B Q
0 0 1
0 1 0
1 0 0
1 1 0

Now when A (the LFO) is 0 the output is 1.
When A is 1 the output is 0.

With XNOR...

A B Q
0 0 1
0 1 0
1 0 0
1 1 1

Same result.

So in both circumstances the clock is just being inverted and the sequencer advances (albeit a half cycle out of phase).

[ColinP]

Also if your intention is for the LFO to control the tempo of the sequencer you need to feed its output to the sequencer's EXT CLK socket and engage the EXT button as shown below.

lfoAsClock.png (266 KiB) Viewed 233 times

You could then add an AND gate into this path to enable or disable the LFO's external clock signal (which is what I'm guessing you were experimenting with).

In your screenshots the LFO is just starting the sequencer and the sequencer is running on its own internal clock. So the only impact the LFO RATE knob will have is how quickly the sequencer starts.

[Xeys42]

Thanks for replies ColinP. No that wasn't my intention although I will try that.

So in both circumstances the clock is just being inverted and the sequencer advances (albeit a half cycle out of phase).

So from what I understand the LFO inverts the signal? can you expand on this a little more if you don't mind.
Edit: How did I miss that, penny drop moment. Of course the LFO is cycling on and off, D'oh!

[ColinP]

Hi, I hope my posts helped a bit.

The inversion is caused by the NOR or XNOR gates.

The little circle on the output of a logic gate symbol indicates that logical inversion (NOT) is applied to the output so that's one way to understand that a NAND gate is an AND gate followed by an inverter, a NOR gate is an OR gate followed by an inverter etc.

Unfortunately XNOR has come to be used for what I think ought to be called an NXOR gate so this adds a bit of confusion.

Ah, so I'm guessing you were just using the Mini LFO as a source of a test pulse. You might find this module useful...
https://store.cherryaudio.com/modules/buttons-21

Roland (P. Moon) kindly published this for free years ago and I think virtually everbody uses it in test rigs.

[Aarnville]

All of that stuff is why I made the Transporter module. I was spending too long fiddling with logic gates just to start and stop a couple of sequencers.
I originally made it just for myself but it turned out to be one of my bestsellers!

[Xeys42]

Thanks ColinP, yes they did help. I will try the buttons module, I downloaded it recently.

The inversion is caused by the NOR or XNOR gates.

Now I'm more confused. If this is so it sounds to me like they are doing what they shouldn't be. I give up, lol. I think you had the right idea Aarnville.

[utdgrant]

The inversion is caused by the NOR or XNOR gates.

Now I'm more confused. If this is so it sounds to me like they are doing what they shouldn't be. I give up, lol.

No, they're working fine. It's the fact that there is no signal connected to the right-hand input of the logic gates which explains Colin's thinking. This is equivalent to the 'B' input in any truth tables always being '0' or 'Low'.

The OR and XOR gates function as buffers of the left-hand (or 'A') input.
The NOR and XNOR gates function as invertors of the left-hand (or 'A') input.

OR-XOR-NOR-XNOR.jpg (132.91 KiB) Viewed 10 times