ASCII: 0x2n: <blank> ! " # $ % & ' ( ) * + , - . / 0x3n: 0 1 2 3 4 5 6 7 8 9 : ; < = > ? Look familiar? This is called a bit-paired keyboard

ASCII: 0x2n: <blank> ! " # $ % & ' ( ) * + , - . / 0x3n: 0 1 2 3 4 5 6 7 8 9 : ; < = > ? Look familiar? This is called a bit-paired keyboard¹ — every pair (or triple, in the case of control characters) of characters on a key differ in encoding by flipping one bit, which is relatively easy to do in hardware. The ADM-3A had no processor. ¹ https://en.wikipedia.org/wiki/Bit-paired_keyboard https://en.wikipedia.org/wiki/Bit-paired_keyboard