Printing ASCII Characters > 127 Fails in CGA Mode

MS-DOS                      | WINDOWS

The information in this article applies to:

• The C Run-time (CRT) included with:

      - Microsoft C for MS-DOS, versions 5.1, 6.0, 6.0a, and 6.0ax
      - Microsoft C/C++ for MS-DOS, version 7.0
      - Microsoft Visual C++ for Windows, versions 1.0 and 1.5
  

When a CGA graphics card is in any CGA graphics mode it does not display ASCII characters greater than 127 when Microsoft C text-output routines are used. Garbage characters are displayed instead.

This is expected behavior. The default character-definition table for CGA graphics cards contains only the first 128 ASCII characters. To print ASCII characters 128 to 255, a separate character-definition table must be set up and accessed through Interrupt vector 1FH. The MS-DOS utility GRAFTABL leaves such a table and hooks the Interrupt 1FH vector to point to it.

For more information, see Richard Wilton's book "Programmer's Guide to PC & PS/2 Video Systems," page 269, which is available from Microsoft Press.