Multiple RC522 RFID reader on Arduino Mega

Hi all,

I just want reconfirm that all digital i/o on the Arduino Mega board can be used to connect RC522 (SS pin) right? Except the pins on board that are used to connect MOSI,MISO and SCK. Because i want to figure out how many readers Arduino Mega 2560 can support.

Are you going to use any other interface? Serial, so you can talk to a PC? I2C so you can display on an LCD? If not, it looks like 51 is the limit: 54 digital I/O pins minus SCLK, MOSI, and MISO. You might need drivers on SCLK and MOSI to drive the 51 inputs from one output.

You could also use your choice of output expansion (shift registers, port expanders) to get even more SS pins on an UNO or Nano. Eight shift registers will use three pins of an UNO or Nano to get 64 output pins.

thank you so much sir. You really answering my question.