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by exmadscientist
2186 days ago
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There's actually five of them, not just one: the ’57, ’58, ’97/’157, ’98/’158, and ’99. (Plus four more if you count the open-drain-output types released only by Fairchild, but I don't as they're too annoying to source reliably.) These guys are super useful. Unfortunately it's somewhat unobvious how best to use them, since the manufacturer literature is written in a very obtuse way. Except for the ’99, they're all just two-input multiplexers. Some have an input inverted and some have an output inverted. The ’99 adds an output enable line and a fourth input, which it XORs with the output. It's much easier to design with these things when you think of them as multiplexers! I've made a nice chart that I use to help design with these parts, but it's on my work machine and I'm too lazy to log in on a weekend to retrieve it. I've made a lot of nice charts and references... I should figure out somewhere to publish them.... Page 5 of this old NXP PDF was the starting point I used: https://www.avnet.com/wps/wcm/connect/onesite/8100cb9c-39d1-... but I removed the redundant entries (most of us know how logic families work by the time this chart is useful...) and added the descriptions of what the parts really are inside. |
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The open drain ones make good level translators as well, since the output can be pulled up to a different voltage. If you find that chart, I’d love to see it!