ASCII-based keyboards have a key labelled "Control", "Ctrl", or (rarely) "Cntl" which is used much like a shift key, being pressed in combination with another letter or symbol key. In one implementation, the control key generates the code 64 places below the code for the (generally) uppercase letter it is pressed in combination with (i.e., subtract 64 from ASCII code value in decimal of the (generally) uppercase letter). The other implementation is to take the ASCII code produced by the key and bitwise AND it with 31, forcing bits 6 and 7 to zero.