Path: utzoo!utgpu!jarvis.csri.toronto.edu!rutgers!ucsd!ogccse!blake!dlear
From: dlear@blake.acs.washington.edu (Dale Lear)
Newsgroups: comp.sys.ibm.pc
Subject: 8 mhz "turbo" mode problem
Message-ID: <3578@blake.acs.washington.edu>
Date: 12 Sep 89 04:19:26 GMT
Reply-To: dlear@blake.acs.washington.edu (Dale Lear)
Organization: University of Washington, Seattle
Lines: 67

8 mhz "turbo" mode problem

     I'm having trouble with an XT clone when using it in 8mhz "turbo"
mode.  While working away at 8mhz the keyboard shift status byte 
(Ctrl/Shift/Num lock/Scroll lock) seems to get randomly set.  When 
this happens I might type "abc" but the program I'm using will 
think I've typed "^A^B^C", "ABC", or "alt-A alt-B alt-C".  I have 
experienced this problem with a wide variety of programs but using a 
Borland product seems to exacerbate the trouble.  This problem *never* 
manifests itself when I run at 4.77mhz.

    If I'm lucky enough to be able to get to a DOS prompt and the caps 
bit is the one that's set, I can fix the problem by running the 
following batch file which clears the keyboard status byte at 0:417.

FIXIT.BAT
   mode mono
   mode com1: 1200,N,8,1
   c:\dos\debug < c:\bat\fixit.dbg

The file FIXIT.DBG contains:
   e 0:417 00
   q

On *rare* occasions, just waiting a few minutes will correct the 
problem.  If I can't run FIXIT (i.e., DOS thinks I'm trying to run a 
program called ^F^I^X^I^T) and waiting doesn't work then I'm forced to 
reboot.  Pressing the Caps Lock/ Scroll Lock/ Num Lock/ Shift keys has 
no effect.  I've experienced the problem while using different 
keyboards so I don't think it's the keyboard's fault.

    I use the following programs to switch CPU speeds.

8MHZ.COM  (all numbers are in hex)
   IN   AL,61                              
   OR   AL,04                              
   OUT  61,AL                              
   XOR  AX,AX                              
   INT  21                                 

477MHZ.COM  (all numbers are in hex)
   IN   AL,61                              
   AND  AL,FB                              
   OUT  61,AL                              
   XOR  AX,AX                              
   INT  21                                 

     Just for the record; the mother board is a no-brand-name Taiwan 
made job called a "TURBO-640", the CPU is an 8mhz rated NEC V20, the 
ROM BIOS is a true blue IBM BIOS dated Monday, August 16, 1982, and 
I'm using MSDOS 3.30.  Finally, CONFIG.SYS contains:

   shell=c:\command.com /p /e:512
   device=c:\dos\ansi.sys
   files=24
   buffers=24
   fcbs=32,32

     If you have any suggestions or ideas please let me know via
e-mail as I don't usually read this group.  If somebody is tells me how 
to fix the problem I'll post the solution.

Thanks.

-- Dale Lear

e-mail address:  lear@kaleetan.ms.washington.edu