Serial Link, Hard Wired and UCP

Dear all expert

I am confused with the word serial link, hard wired, UCP

let say

1. the instrument transmitter is using 4-20 ma HART, this is serial link or hard wired?

2. If the transmitter is using Foundation Field bus, it is serial link or hard wired?

3. Signal for a level switch to DCS is serial link or hard wired?

4. Mod bus is a type of hard wired or serial link?

5. What is the different between DCS and RTU?

6. Does PLC based local control panel is same with UCP, what is the different?

Thanks