I used NModbus to create slave device communicating by 1Mbit serial interface. I hoped to have very fast communication but delay between master request end and slave response start is about 3-4 ms and it is too long. Changing serial port timeout to 0 didn't affect significantly, it reduced the delay to 2.5-3.5 ms.

How can I change timings to have immediate response (at least below 1 ms)?