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Q75095: CLS Does Not Clear Screen on AT&T 6300

Article: Q75095
Product(s): Microsoft Disk Operating System
Version(s): MS-DOS:5.x,6.0,6.2,6.21,6.22
Operating System(s): 
Keyword(s): 
Last Modified: 17-DEC-2000

-------------------------------------------------------------------------------
The information in this article applies to:

- Microsoft MS-DOS operating system versions 5.0, 5.0a, 6.0, 6.2, 6.21, 6.22 
-------------------------------------------------------------------------------

SYMPTOMS
========

After starting an AT&T 6300, MS-DOS uses only one line of the screen to
display commands such as DIR, TREE, and so on; however, the startup information
remains on the screen even after issuing the CLS command. In the other cases,
the system will hang at the DOS prompt after pressing ENTER a few times.

WORKAROUND
==========

To work around this problem, add the following line to the CONFIG.SYS file, or
use the debug script listed below.

     device=ansi.sys /s

The same behavior occurs on AT&T 6310 machines.

MORE INFORMATION
================

The ANSI.SYS /S switch is an undocumented switch that will force the video to
display in 25-line mode. MS-DOS 5.0 or 6.0 relies on byte 40h:84h of the BIOS to
work in 43/30 line mode. The earlier version of MS-DOS did not use this byte.
The following is a short program to patch the BIOS area into having the 25
(actually 24, because it is is 0-based) value required for a CGA/MDA adapter.

At the DOS prompt, type "debug" (without the quotation marks).

You will then see the Debug prompt (a hyphen). Type the following, pressing ENTER
after each line:

Debug              User
Response           Input
--------           -----

C:\>               debug
-                  n patch.com
-                  a
xxxx:xxxx          mov ax,40
xxxx:xxxx          mov es,ax
xxxx:xxxx          es:
xxxx:xxxx          mov byte ptr [84],18
xxxx:xxxx          int 20
xxxx:xxxx          <press ENTER>
                  <press ENTER>
-                  r cx
:                  d
-                  w
-                  q

This will create PATCH.COM, a file you can execute from the command prompt. If
the problem is resolved, put an entry to execute the PATCH.COM file in the
AUTOEXEC.BAT file.

Additional query words: 6.22 boot ATT att6300 scroll scrolling 5.00 5.00a 6.00 6.20

======================================================================
Keywords          :  
Technology        : kbMSDOSSearch kbMSDOS621 kbMSDOS622 kbMSDOS620 kbMSDOS600 kbMSDOS500 kbMSDOS500a
Version           : MS-DOS:5.x,6.0,6.2,6.21,6.22

=============================================================================

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