5V system and 3.3V system level translation

When designing a circuit with an MCU or arm system, it is 3.3V to meet the MCU's VCC, but the peripheral circuit needs 5V. Sometimes it's the reverse. Although the MCU's IO now claims to support TTL level, but we do not want to connect the MCU IO port directly on the 5V, even if the IO Port first series A resistor, and then connect 5V, so always worry about burning the MCU, again, the MCU claims that the IO port supports TTL level, But not all Io is like this. There is a hidden danger anyway.
The solution is level shifting.
Specifically, I only said that I used the method in the actual project, and the use of the project is more convenient, the others are no longer said.
The first type: the use of OC or OD gate circuit, so that the collector or drain can be pulled through a resistor to a new VCC, the base or gate can be connected to another VCC, so that the realization of the 3.3V control 5v,12v level signal output. Note that there is a need to choose a good resistance resistor, but also to consider the Mcuio drive capacity. This type of circuit is mostly used in the output circuit of the level conversion circuit.
The second is to convert the 3.3V and 5V using a specific level-shifting chip. For example 74lvc4245a,74alvc164245 These two chips are used more.



is the 74lvc4245a chip pin diagram and the specific electrical meaning, it exists 5VVCCA and 3.3vvccb,2 power supply pins, so that can achieve 5V and 3.3V conversion, and dir control data direction, this also achieved 3.3V to 5V, and 5V to 3.3V two direction conversion. In addition, the 74lvc4245a can also increase the Mcuio current drive capability. I would prefer this chip if I needed it in the design. 74alvc164245 is 16Bit, function and 74lvc4245a almost.
Of course, there are other level-shifting scenarios, but comparisons, often used, or both methods are the most practical. This enables the 3.3v pin to be used to control the 5V level.
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5V system and 3.3V system level translation