What is extended 7-bit (or 8-bit) code?

Question

I just started reading the ECMA-48 standard (ISO/IEC 6429), and have a question.

It says:

This Ecma Standard defines control functions and their coded representations for use in a 7-bit code, an extended 7-bit code, an 8-bit code or an extended 8-bit code.

What does the "extended" 7/8-bit code mean here?

Answer 1

ECMA-35 talks about these. These terms are key:

code extension: The techniques for the encoding of characters that are not included in the character set of a given code.

escape sequence: A string of bit combinations that is used for control purposes in code extension procedures. The first of these bit combinations represents the control function ESCAPE.

Character ESCAPE: ESCAPE is a control character used for code extension purposes. It causes the meaning of a limited number of the bit combinations following it in a CC-data-element to be changed. These bit combinations, together with the preceding bit combination that represents the ESC character, constitute an escape sequence.

Thus, what we have here is a system where you can switch encoding systems in the middle of your text: You can start a text using Latin-1 encoding, provide an escape sequence that switches to Latin-2, and continue your text. ECMA-35 talks about this in appendix A. Chapter 13 has more information about the structure of escape sequences.