CLS Does Not Clear Screen on AT&T 6300 (75095)
The information in this article applies to:
• Microsoft MS-DOS operating system 5.0
• Microsoft MS-DOS operating system 5.0a
• Microsoft MS-DOS operating system 6.0
• Microsoft MS-DOS operating system 6.2
• Microsoft MS-DOS operating system 6.21
• Microsoft MS-DOS operating system 6.22
This article was previously published under Q75095
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.
To work around this problem, add the following line to the CONFIG.SYS file,
or use the debug script listed below.
The same behavior occurs on AT&T 6310 machines.
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
You will then see the Debug prompt (a hyphen). Type the following,
pressing ENTER after each line:
- n patch.com
xxxx:xxxx mov ax,40
xxxx:xxxx mov es,ax
xxxx:xxxx mov byte ptr ,18
xxxx:xxxx int 20
xxxx:xxxx <press ENTER>
- r cx
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.
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