Minor bugging me problem: how is screen update with this speed possible?

[rud01f]

Recently, I started to look through how communication with Turing Screen is done.
I've noticed it's done by opening serial communications port with 112500 baud rate (which is at most 112500 bits per second).
Then by curiosity I did the math and noticed something odd, which is still bugging me to this moment.

My 3.5" Turing Screen is 320x480 16-bit pixels. Which results in 320 * 480 * 16 = 2457600 bits.
Thus, the screen drawing process (initial whole background) should take at least 2457600 / 112500 ~= 21,84 seconds.
The real update process is no longer than 2-3 seconds.
But I cannot find where I'm wrong. The only explanation the serial post speed it bigger than declared.
Any big mind could help me please?