Difference between Jtag and RS-232 TTL interfaces?

Question

JTAG

Good evening,
I immediately apologize if the question sounds strange, but I can’t understand what is the fundamental difference between these two (or three) technologies. As I currently understand it.
Jtag is a physical interface and protocol used for programming and debugging microcontrollers.
RS-232 protocol is also sometimes used to work directly with microcontrollers.
There is also something like TTL , but here I was completely confused, earlier, to restore the controller on the hdd, a cable with an RS-232 TTL chip was used through which it was possible to connect and reflash this board ... after which the screw continued to work successfully.

Answer 1

Horse people mixed up.
there is a UART (RS-232 as you called it) in fact it is 3 wire ground rx tx requires a working chip, or bootloader.
UART can have several voltage levels, that's it (TTL 0.3v zero 2.4 unit)
There is also 5V tolerance, that is, it is powered by 3.3 but is able to digest 5V
JTAG allows you to connect to a non-working device and fully control the process of its operation