Matrix-scan keyboards allow for an unlimited number of overlapping keystrokes, but that allowance requires per-key diodes to prevent ghosting. Inexpensive keyb

Matrix-scan keyboards allow for an unlimited number of overlapping keystrokes, but that allowance requires per-key diodes to prevent ghosting. Inexpensive keyboards often forego the per-key diodes in favour of cheaper/thinner construction, and to prevent phantom inputs the controller registers nothing when the matrix scan shows keypresses that might be the result of ghosting.