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Author Topic: simple logic gate usage  (Read 2756 times)

trials_modder

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simple logic gate usage
« on: May 01, 2007, 03:10:54 AM »

hi
i'm wondering how to use the 4000 series and 74* logic gates. from the data sheets i've established where Vcc and ground are hooked up, where to hook up the actual inputs/ouput for a single gate, but when i check the output with my multimeter the results aren't expected.
btw, i'm using the 4081 AND and the 74Ls00 NAND gates for testing

to make that clearer - how do i design the inputs so they can switch between a high and low state? i can physically move the input wire between + and gnd, but i don't want to do that

after much googling, i think i got it:

http://www.allaboutcircuits.com/vol_6/chpt_7/2.html
« Last Edit: May 03, 2007, 06:30:11 PM by viridius »
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viridius

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Re: simple logic gate usage
« Reply #1 on: May 03, 2007, 06:32:26 PM »

Some logic design tips:
Regulate and decouple your power supply with a voltage regulator chip and a capacitor.
Tie the inputs of unused gates high or low (don't let them float).
Use pull-up or pull-down resistors (also to avoid floating inputs).
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trials_modder

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Re: simple logic gate usage
« Reply #2 on: May 03, 2007, 11:42:15 PM »

yeah, i seem to be having troubles combining a CMOS and TTL logic gate together, I think I"ll just go buy some CMOS equivalents of the TTL chips to make things easier :p
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rafununu

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Re: simple logic gate usage
« Reply #3 on: May 04, 2007, 05:08:50 AM »

Don't forget, always connect inputs either to GND or VCC, even through a resistor. Concerning TTL and CMOS, CMOS inputs are TTL compatible provided supply doesn't exceed 5V.
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trials_modder

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Re: simple logic gate usage
« Reply #4 on: May 04, 2007, 11:35:06 AM »

ok, i'll take another stab at building the circuit. should there be any special connections (pulldown resistors?) between the TTL output and CMOS input, or will TTL act as ground?
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