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I need a thing (preferably a single IC) that has 8-bit input, 8-bit output and a control bit, with this behaviour:

  • If the control bit is active, set output bits to the inputs (no need to actually conduct through, as long as they have the correct (0-5 V TTL compatible) signals.

  • If the control bit is inactive, set output pins to high impedance so they don't interfere with other stuff.

So essentially a "bus output enable/disable gate".

I don't seem to find any; maybe I'm searching for the wrong keywords. Anyone have an idea?

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    \$\begingroup\$ You're looking for an "octal buffer with enable". Which one depends on what logic standard, data rate, etc. \$\endgroup\$
    – The Photon
    Commented Jan 29, 2018 at 17:59
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    \$\begingroup\$ Start with looking at what an HC541 (for instance) does. Is that the sort of thing you want? If so, then just need to find the right family. If not, then you need to explain why not, as your question may be asking for the wrong thing. \$\endgroup\$
    – Neil_UK
    Commented Jan 29, 2018 at 18:02
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    \$\begingroup\$ A transparent latch will work. eg 74HC573 \$\endgroup\$
    – Trevor_G
    Commented Jan 29, 2018 at 18:06
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    \$\begingroup\$ @nonchip, it's a buffer because it might have higher output current capability than other logic chips. That won't hurt you if you don't need it, though. \$\endgroup\$
    – The Photon
    Commented Jan 29, 2018 at 18:24
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    \$\begingroup\$ yeah, this meaning of buffer is an amplifier with voltage following and current gain. \$\endgroup\$
    – Jasen Слава Україні
    Commented Jan 29, 2018 at 19:06

3 Answers 3

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It sounds like you want an octal buffer with tri-state output.

For your 5 V application, a device such as a 74HCT245 will do it.

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That is called a "buffer". Most have enable inputs that do what you want. 8 bits are available in a single IC, which would be called a "octal buffer".

These were very common in bus-oriented systems back when logic meant a bunch of 74xxxx chips on a board. Fortunately, we moved out of caves, ditched the low-function logic chips, created indoor plumbing, and invented sliced bread. Life is better today.

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    \$\begingroup\$ actually that's exactly what I need them for: I want to build a Z80 based parallel bus oriented computer :D \$\endgroup\$
    – nonchip
    Commented Jan 29, 2018 at 19:02
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I like the good old 573 because the latches can be transparent or not: -

enter image description here

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  • \$\begingroup\$ for the case I have in mind (putting dip-switched addresses onto the bus on a single signal) I need no latching at all, but I'll keep those in mind, pretty sure I'll need other buffers in this or similar projects \$\endgroup\$
    – nonchip
    Commented Jan 29, 2018 at 19:10
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    \$\begingroup\$ The latching is transparent if you set LE high. \$\endgroup\$
    – Andy aka
    Commented Jan 29, 2018 at 19:24
  • \$\begingroup\$ yep I saw that, it's just I don't need any latching (as far as I know so far, still an ongoing design), so I guess I'll pretty much select the part by price there. But if I'll need latching buffers at some other point (likely) I'll remember your recommendation :) \$\endgroup\$
    – nonchip
    Commented Jan 29, 2018 at 19:34
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    \$\begingroup\$ The '573 is also good because it doesn't have a crazy pinout. \$\endgroup\$
    – pipe
    Commented Jan 29, 2018 at 22:38

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