The 74HC is an 8-bit transceiver IC with 3-state output. Meaning it has two set of pins A0-A7 and B0-B7 , in which each set has 8 pins. Out of these two sets one set can be used as input and the other set can be used as output. Since the IC is a transceiver IC, Data can flow from input bus to output bus and also from output bus to input bus, by simply toggling the Direction pin DIR pin as required.
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Reading the datasheet of the 74HC, the input high threshold is 2. This will not work reliably. As an alternative to using the HCT chip, you could consider something like the 74LVCA, which is an octal transceiver with voltage translation.
That particular one has a 3. Many voltage translating types can avoid certain problems with power domain sequencing. With the HCT option you have to ensure the 3. From the 74LVC8T datasheet :. The devices are fully specified for partial power-down applications using IOFF.
The IOFF circuitry disables the output, preventing any damaging backflow current through the device when it is powered down. Maybe the following is the solution for you. I just found this when I searched for a level shifter. And after I found that I found your question. That is a commercial product from a reputable Thai electronic component supplier.
I didn't try it myself. It seems you just have connect DIR to 3. Problem solved. You can download the data sheet with more info on that page. I just looked a little on the internet. Here is the ready build circuit with English description. Sign up to join this community. The best answers are voted up and rise to the top.
Home Questions Tags Users Unanswered. Driving a 74HC in one direction with 3. Asked 4 months ago. Active 4 months ago. Viewed times. I now have to switch to a 3.
Will I be able to get away without any logic level adjustment circuitry? Active Oldest Votes. Elliot Alderson Elliot Alderson Andy aka Andy aka k 15 15 gold badges silver badges bronze badges. The performance is generally higher as well, being a newer logic family. Maple 7, 2 2 gold badges 6 6 silver badges 27 27 bronze badges. Spehro Pefhany Spehro Pefhany k 9 9 gold badges silver badges bronze badges.
This is just one circuit. In the download below you will find similar with 5V and 3. Edgar Edgar 8 8 bronze badges. However it is not what I am after. The circuit you post with Dir pulled high has the 5V logic changing into 3. I need it the other way around ie.
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