4 ms·
You seem to know what's going on, do you mind answering a question about the schematic? If the transistor is a PMOS like the author says, when the output of th
by moefh 6y ago
You seem to know what's going on, do you mind answering a question about the schematic?
If the transistor is a PMOS like the author says, when the output of the NAND goes low wouldn't both the LED and the transistor turn on?
The way the LED is drawn it should turn on when the NAND output is sinking current, right? Maybe the LED is drawn upside down? Or am I misreading/misunderstanding something really simple?
- exmadscientist 6y agoIt's not clear what's going on with the LED in the article's schematic, because only one side of it is connected. Depending on how the other side is tied off -- you can tie it to VDD or to ground -- you can get "lit high" or "lit low" behavior out of it. (And, of course, the polarity might be reversed. LEDs are notorious industry-wide for having confusing polarity markings. So never, ever assume a LED is the right way around....) That's because this NAND gate is quite good at either sinking or sourcing current: 24 mA either way (at 3.3V). Older designs are not so balanced, or capable of so much current. (The LVC family is often chosen for exactly this reason.)
- moefh 6y agoThank you, that clears things up.