What options do I have to perform level shifting from 5 V to 3.3 V and vice versa?

The following figure shows level shifting from 5 V to 3.3 V and from 3.3 V to 5 V.

Down translation (High-to-low voltage level translation):
The input-tolerant function allows level shifting from a higher voltage to a lower voltage such as from 5 V to 3.3 V. For example, the input-tolerant function allows 5 V to be applied to an input without drawing extra current even when V_CC = 0 V.

For down translation using the input-tolerant function of a CMOS logic IC, ensure that the maximum low-level input voltage is within the V_IL range.

Up translation (Low-to-High voltage level translation):
Level shifting from a lower voltage to a higher voltage such as from 3.3 V to 5 V can be performed if the high-level output voltage (V_OH) of the driving IC satisfies the high-level input voltage (V_IH) of the driven IC because V_OH is almost equal to the supply voltage (V_CC).
Since the minimum high-level input voltage (V_IH) of typical CMOS logic ICs is specified as V_CC × 0.7, V_IH is 3.5 V when V_CC = 5 V. Therefore, if the V_OH of the driving IC is 3.3 V, the minimum V_IH of the driven IC is not satisfied. In this case, consider using a CMOS logic IC with a TTL input.

The following shows the specifications of the TTL input of the 74HCT240. Since its minimum high-level input voltage (V_IH) is 2.0 V, the 74HCT240 allows up translation from 3.3 V to 5 V

The 74VHCT240 cannot be used if the supply voltage of the preceding IC is lower than 2 V. In that case, it is necessary to use a level shifter.

There is also a method of Up translation using a product with open drain output. Due to the pull-up resistor R_pull, the output swings to the V_CC level.