What is the symbol for R? Why resistors on the connector output?

Question

Electronics

1. Connecting the J-tag interface to the MK. What is the symbol for a resistor?

2. This is an example of a completed task (possibly incorrect). Here are other denominations for R. How are they chosen?
And yet, everywhere resistors with a dissipation power of 0.125 watts. Why? For what? Why are they like this?

3. And this is the end of the connector, through which the J-tag interface is actually connected to the MK. Why is a resistor connected to the ground output through one?


Thank you all in advance for your help!

Answer 1

1. This is a resistor assembly. A pack of 10 kilo-ohm resistors in one case.
2. Resistors are selected based on the calculation. Usually for TTL circuits, pull-up resistors are taken 10k, for CMOS - 100k. The power of the resistor is chosen again based on the calculation - they take 2x - 3x the power reserve that will be allocated on this resistor. P = U ^ 2 / R
3. You need to look at the entire scheme, and not a stub.

Answer 2

These are resistors of the so-called galvanic isolation. They are used to reduce the influence of output circuits on each other.