[knc1]

Your post before last -
The one showing you using a test program while the serial lines where loop'd back -
The picture of it failing . . . .

Use the terminal emulator for your testing, the **same** terminal emulator that you will be using to type to the Kindle with.
The objective is to see if everything from the Tx - Rx loopback is working.
We are not concerned if some test program works or not.

This set-up of a low voltage serial port is something that works for everyone else in the world, except you.
That tells me where the problem lies, your doing something that you have not explained which makes it fail.

Re-check your work, again and again until it works in loop-back mode.

Then it will work with the Kindle, just by removing the Tx <-> Rx loopback - - **IF** the serial port on the Kindle is good.

PS: Is this the kindle that had its serial port connected directly to the PC's high voltage com port?
If it is, then the chances that the Kindle's serial port is bad is very real.

That serial port (and any of the 3v3 CMOS parts) can be ruined just by static electricity on the body when you touch a connection. You have never mentioned if you are following all recommended anti-static conditions.
Since you live in an area which is hot and dry, that is also a very real concern.

Other than those things, I have no ideas at all, other than the problem is at your end of this conversation.