I have to read 64 digital inputs using the MEGA2560. So I am thinking about using a parallel to serial
converter to convert all the 64 inputs to a serial stream using a shift register. And then read the serial data out of the shift register using the MEGA2560.

Has anyone done this?
Is there any pins on the MEGA2560 that I can use to do this?




Why ? The Arduino Mega 2560 has 54 digital pins plus 16 analog/digital pin, that is a total of 70 digital input/output pins.

Pin 0 and 1 are used for the serial communication to the computer.
Pin 20 and 21 are the I2C bus.
Then you still have 66 digital pins.