Logic gates without transistors?

i don't see how both diodes either and being triggered would not pull high to low? both diodes would do the same? i don't get how AND is made?

I cant see what your talking about but

if 4 or 5 is low, then current is sinked thus logic = low

if both are high then current sinks though 1, thus logic = high

Are you referring to the classic wired-AND gate using two diodes and a resistor pull-up?

http://upload.wikimedia.org/wikipedia/commons/thumb/9/9d/WiredAND.svg/220px-WiredAND.svg.png

Two high inputs equal a high output, either (or both) inputs low equals a low output, that statisfies the classic AND truth table.

Then you can contrast that with the classic wired-OR gate:

http://upload.wikimedia.org/wikipedia/en/8/82/WiredOR.JPG

Lefty

Sorry, the image was not showing.... what's going on with those 2 diodes and pull up, so there's always 9v high ...

I would presume either not both but either of the diodes would pull it ground? not both like an AND logic calculation

cjdelphi: Sorry, the image was not showing.... what's going on with those 2 diodes and pull up, so there's always 9v high ...

I would presume either not both but either of the diodes would pull it ground? not both like an AND logic calculation

You don't seem to understand how a truth table works. Just map out the four possible input voltage combinations (low-low, low-high, high-low, high-high) that are possible and the resulting voltage output for each of the conditions and see if you can't spot the AND function after all.

Lefty

[path deleted - seems to have been hijacked by a semi-porn site - Moderator]

if pin 11 and pin 14 are low (B and C of the binary output)

Reset triggers, but i don't understand why this circuit ONLY triggers off when both B and C are LOW, i don't understand why would it not tigger off if B was low and C was high? B would provide a low signal to trigger reset? how's the AND part to this circuit working via the 2 diodes and a pull up?

But it is an AND. Look at the truth table:

In1 In2 Out 0 0 0 0 1 0 1 0 0 1 1 1

Thus Wired AND - both inputs must be High for output to be High.

If Both needed to be High to make the output Low, that would be a NAND - if you were to take that output and invert it using a NPN collector follower,

In1 In2 Out 0 0 1 0 1 1 1 0 1 1 1 0

And there's Wired OR, with diodes flipped around - either input High makes outpt High: In1 In2 Out 0 0 0 0 1 1 1 0 1 1 1 1

If you were that output and invert it using a NPN collector follower, then you have NOR:

In1 In2 Out 0 0 1 0 1 0 1 0 0 1 1 0

In all cases, the diode serve to isolate the inputs from each other.

If either but not both were to affect the output, that would be Exclsive OR, XOR:

In1 In2 Out 0 0 0 0 1 1 1 0 1 1 1 0

XOR/XNOR more difficult to pulloff with just diodes & resistors tho.

and inverted, XNOR

In1 In2 Out 0 0 1 0 1 0 1 0 0 1 1 1

Generally, Wired OR and Wired AND are all that's needed - if any of several inputs go low, the output goes low - such as with a keypad, pressing any key to Gnd can be used to create an interrupt and tell the code to go scan the keypad.

If you want action only with 1 or the other, that's easier to mimic in software - similar example, with multiple keys pressed, scan the inputs, if more than 1 was pressed, ignore the result.

For historical reference, the diagram in reply #2 is probably about the very first AND
gate ever invented. Since you can’t make a very good computer that way [ie, it loses
noise margin after about 3 gates in series], they added an NPN inverter to it’s output,
and invented the modern computer world, starting from there.

http://www.google.com/search?&site=imghp&tbm=isch&source=hp&biw=1033&bih=858&q=diode+transistor+logic

yes, you can only do rather simple things with diode logic (though its fun to mess with)

Which came first, diode logic or relay logic?

I would guess relay as it was introduced into practical application about 60 years before the diode (in practical application)

I had a calculator once that was entirely diode logic, there must have been 1000s of them plus some magnetic core memory as well and to top it off a nixie display.

I hope I've still got it somewhere.

As for relay logic, we built an entire runway lighting system using relay logic, flip flops, NAND, AND, OR gates etc were each a large PCB. All at 48V IIRC.


Rob

westfw: Which came first, diode logic or relay logic?

http://www.thocp.net/biographies/shannon_claude.htm

westfw: Which came first, diode logic or relay logic?

Yeah, I knew someone would bring this up, ;-).

Osgeld: I cant see what your talking about but

if 4 or 5 is low, then current is sinked thus logic = low

if both are high then current sinks though 1, thus logic = high

That diagram reminds me of the logic gates used in the Apollo Guidance Computer.....

Krupski:

Osgeld: I cant see what your talking about but

if 4 or 5 is low, then current is sinked thus logic = low

if both are high then current sinks though 1, thus logic = high

That diagram reminds me of the logic gates used in the Apollo Guidance Computer.....

Houston, we have AND problem...

majenko: Houston, we have AND problem...

Just for that, you go do another lap around the Moon.

[quote author=Runaway Pancake link=topic=155918.msg1170216#msg1170216 date=1364131240]

majenko: Houston, we have AND problem...

Just for that, you go do another lap around the Moon. [/quote] Hey - I am the centre of the universe. The Moon does laps around Me! :P

majenko: [quote author=Runaway Pancake link=topic=155918.msg1170216#msg1170216 date=1364131240]

majenko: Houston, we have AND problem...

Just for that, you go do another lap around the Moon.

Hey - I am the centre of the universe. The Moon does laps around Me! :P [/quote]

The universe is rotating? Reference? ;)

afremont:

majenko: [quote author=Runaway Pancake link=topic=155918.msg1170216#msg1170216 date=1364131240]

majenko: Houston, we have AND problem...

Just for that, you go do another lap around the Moon.

Hey - I am the centre of the universe. The Moon does laps around Me! :P

The universe is rotating? Reference? ;) [/quote]

What if the universe is just a bubble a 5 year old is blowing just waiting to get big enough to BOOOOOOOOM.......