Raghav,

Raghav Gururajan wrote:
> So I did "sudo cat /dev/ttyS4" in the terminal. After 10 
> seconds, the
> cursor blinking stopped,

This is probably just your terminal emulator helpfully stopping 
the cursor blink after 10 ‘idle’ seconds to save a tiny bit of 
power, not related to the serial port.

> then I touched the screen with the pen, it
> started giving output non-stop. Like the output never stopped, I 
> had to
> close the terminal.

It's not what I'd naively expect, but sure.  Maybe the protocol 
expects some kind of ACK and keeps retransmitting otherwise. 
Maybe the protocol's weird.

> Is this a good sign that my touch screen is
> attached to serial port 4?

Yes!

Kind regards,

T G-R