MODE. Determines the interpretation mode as follows:
0Interprets each byte as a character
1Interprets the next two bytes as a character
2Same logic as mode 0, except that vertical substitutes are used if found in a VT segment of the current font. Characters are rotated counter
3Same input logic as mode 1, except that vertical substitutes are used if found in a VT segment of the current font. Full width characters are rotated counter