It is a basic feature. Are you sure it is not available on your machine. Try this:
Set parameter 3204#2 to 1 (3204#0 should remain 0; status of the other six bits does not affect this feature):
Such a parameter setting displays an extended character set, as soft keys, in the EDIT mode, displaying “(“, “)” and “@”.
With this setting, if square brackets are needed, use the bracket keys on the MDI panel, and if parentheses are needed, do the following (in EDIT mode):
• Press PROG on MDI panel (press PROG again if the current program is not displayed).
• Press the OPRT soft key.
• Press the right extension key (>) twice.
• Press the C-EXT soft key.
After this, soft keys for left parenthesis, right parenthesis, and @ (which can be used in the comments inserted in a program) will appear which can be used as and when required for editing in EDIT mode.