We use good BOURNS type PEC11L Series encoders. They have 100,000 cycles. The manufacturer recommends an external RC filter (see data sheet). The RC filter already has a pullup. Therefore internal pullup resistance is not necessary.
The Teensys inputs for the encoder are operated via built-in pullup resistors.
Pullup resistors are switchable resistors in the IC that switch an input pin to operating voltage.
This means that the input pin is 'active low', so it switches when...