Timeline for When is it appropriate to mix 74LSxx components with original TTL 74xx?
Current License: CC BY-SA 4.0
14 events
| when toggle format | what | by | license | comment | |
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| Dec 13, 2023 at 0:40 | vote | accept | BZo | ||
| Dec 12, 2023 at 15:09 | history | edited | toolic | CC BY-SA 4.0 |
deleted 11 characters in body
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| Dec 11, 2023 at 15:04 | answer | added | Hearth | timeline score: 7 | |
| Dec 11, 2023 at 13:13 | answer | added | SteveSh | timeline score: 3 | |
| Dec 11, 2023 at 12:24 | comment | added | SteveSh | There are some good charts out there that summarize the various issues that have been mentioned above, such as drive strength, input and output voltage levels, speed, etc. So, for a made up example, you may find that in a given use, it's OK to have a TTL device drive an LS device, but not the opposite. | |
| Dec 11, 2023 at 12:04 | answer | added | h22 | timeline score: 7 | |
| Dec 11, 2023 at 9:46 | comment | added | KalleMP | You want to investigate the logic thresholds and sink and source currents to determine more accurately what you might find in a basic fan-out comparison table. This is especially true if you shift to CMOS versions with more equal sink-source. Also static electricity damage thresholds differ. The 4000 series CMOS devices have different pinouts sometimes. At low speeds logic is very forgiving. | |
| Dec 11, 2023 at 5:26 | history | became hot network question | |||
| Dec 10, 2023 at 22:46 | comment | added | Hearth | The speed of later designs (output slew rate, not delay) can also induce ringing and crosstalk issues in poorly laid out boards. | |
| Dec 10, 2023 at 22:43 | comment | added | Hearth | The original 74 series, as well as the S, LS, AS, and ALS series, have limited output drive strength--you can actually drive an LED straight from an output without any current-limiting resistor. The HC, AHC, HCT, AHCT, LVC, ALVC, and AUP series have much stronger output drive, and if put into a design that relied on that limited drive strength you can kill some chips. | |
| Dec 10, 2023 at 22:18 | comment | added | BZo | @Hearth. Thanks for that. When you say drastically different output stage, what does that mean in this context, and how might it interact? | |
| Dec 10, 2023 at 21:45 | answer | added | Spehro 'speff' Pefhany | timeline score: 14 | |
| Dec 10, 2023 at 21:39 | comment | added | Hearth | Bear in mind that any answer to this question will not apply to the currently-easier-to-get 74HC and 74HCT chips--even though the HCT series has compatible logic levels, its drastically different output stage could cause issues. I'm not sure about LS vs original in this regard, which is why this is a comment and not an answer. | |
| Dec 10, 2023 at 21:25 | history | asked | BZo | CC BY-SA 4.0 |