Arduino communication over serial

I am getting the error "Simulink cannot upload data to FOOBAR because it has no input ports".

I am trying to send a constant signal to an Arduino Uno. I am trying to replicate the behavior of a matlab script that cannot be used because I'm using External Mode. The script controls the arduino fine using fopen and fwrite but I do not understand how to implement this correctly using blocks

'serial configuration' and 'serial send'.