Reading port register and print

Question

I am playing with port registers directly to improve speed on a Arduino micro. I have no problem writing them, like

PORTF &= B11101111

However, when I try to read and print it, things get funny and I hope to know why.

Observation 0:

byte dat = PORTF;
Serial.print(dat,BIN);

produces a single 0, where I am expecting 8 0's as for a byte. And, even when I check that a digitalRead correctly gets a 1 from PF5 or A2,

Observation 1:

byte dat = PORTF;
Serial.print(dat,BIN);
Serial.print(dat,BIN);

produces a compiler error like

...cores\arduino\Print.cpp: In function 'println.constprop':
...cores\arduino\Print.cpp:143:1: internal compiler error: Segmentation fault
}
^

Answer 1

The function Serial.print() and it's siblings cuts all leading zeros. So 0b00001111 get's displayed as 1111 and 0b00000000 as 0. So you actually get what you expect. It's just printing different.

Also, when reading PORTF, you actually read the output state of the pins, as you have set it before. If you want to read the real input level of the pins, you should read PINF instead.

Though I don't know, where that segmentation fault came from.