IC enable connection and I2C connection

Using Arduino General Electronics
1

Hi all,

I want to ask how is right to connect enable in ICs and digital communication between ICs.

Take for example this:

In the first case I have a mcu that connect pin1 and pin2 for example, in the second an enable pin, in the third a I2C connection.

I want to ask about this 3 examples:

  • How correctly should I choose the resistors value?
  • It's an error to connect a decoupling cap? (I suppose it's good if I want to have a stable EN but I'll have some delay before EN goes down after my pin5 pull down)
  • What is difference between I2C connection and a simple connection between 2 pins? I see the first have a resistor connected to Vcc and second to Gnd, why this difference?
2

For individual chips' enable lines you read the datasheet - that's always the source of correct
information. If general an input is to be hardwired on a CMOS IC you tie it to GND or Vcc as
appropriate directly. With ancient TTL logic chips things are different, but they are ancient,
you shouldn't be seeing them around these days.

For the I2C bus things are pretty standardized, in the lack of other information use 4k7 pullups
on SDA and SCL.