Author: Paul Mattes

# Square Bracket Characters

## The Problem

Most IBM 3270 emulators have some degree of difficulty with the square-bracket characters, [ and ]. The problem is that there is not a consistent definition of what EBCDIC codes represent them. Hosts may define the square bracket characters as X'BA' and X'BB' (as defined in the IBM Chararcter Set Reference as standard EBCDIC characters), or as X'AD' and X'BD' (which is what the IBM C compilers recognize). In addition, some (but not all) hosts display these characters with a Graphics Escape (GE) sequence. When the host and/or x3270 are misconfigured, the square-bracket characters may be displayed as and , or Ý and ¨.

## Host Configuration

If you are using ISPF, you may simply need to use the correct terminal translation table. According to the IBM's ISPF Planning and Customizing (SC28-1298), Section 3.11, the correct translation table for displaying square bracket characters is called 3278A.

In VM/CMS, the commands terminal apl on and set apl on cause the X'AD', X'BD', X'BA' and X'BB' characters to be displayed with a Graphics Escape (GE) prefix. With terminal apl off and set apl off in effect, they are displayed without the GE prefix.

## x3270 Facilities

x3270 has two facilities to deal with this situation: character sets and keymaps. By selecting the correct character set and keymap, you can set up x3270 to generate and display the proper codes for the square-bracket characters.

> -charset bracket is the default mode, and is used with hosts that use X'AD' and X'BD' for the square-bracket characters. It can be used if the host displays these characters with or without a GE sequence.

> -charset us is for use with hosts that use X'BA' and X'BB' for the square-bracket characters, and do not display these characters with a GE sequence.

> -apl (an abbreviation for -charset apl, -keymap apl) is for use with hosts running APL, which use GE X'AD' and GE X'BD' to represent and display the APL2 square-bracket characters.

Here is a table which summarizes the combinations of characters generated and displayed in the various modes.

| keyboard generates | graphic displayed for EBCDIC codes
x3270 Mode | [ key | ] key | X'AD' | X'BD' | X'BA' | X'BB' | GE X'BA' | GE X'BB' | GE X'AD' | GE X'BD'
-charset bracket (default) | X'AD' | X'BD' | [ | ] | Ý | ¨ |  |  | [ | ]
-charset us | X'BA' | X'BB' | Ý | ¨ | [ | ]
-apl | GE X'AD' | GE X'BD'