Jan's DOS-Based Docking Station

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Abstract

A way to use an old PC as a docking station for your Model 100 or 102 where the laptop controls a completely "headless" (no keyboard, or display) DOS machine. It will probably work with a 200, too.

Introduction

My ideal was that I could transfer files from the laptop to the PC, and back. That's not really a problem: use Desklink and teeny. Configure the PC with DOS, put Desklink in the autoexec.bat and voila: instant TPDD-emulation. If that's all you want, you can stop reading here.

Problem is, what do you do with the files when they are there? Or, how do you get a file from your internet-PC, via the old PC with the TPDD-emulator to the Model T? Typically it's like this: you put the file on a diskette, you attach a keyboard and monitor to the old PC, you boot - interrupting the autoexec - you copy the file in the \ROOT directory, you take keyboard and monitor away again, you boot up, and let Desklink take over the PC. Until the next time you have to transfer a file to or from your laptop. Not practical and a lot of hassle.

So you need a setup to operate in two modes: TPDD-mode, where the PC acts like a TPDD-drive and stores all your files. And CONTROL-mode, where you control the PC to transfer files to and from the outside world. And you need a way to switch from one to the other.

Solve problem one: keyboard and monitor. The hassle of always switching stops the PC from being a real docking station. Of course, you could leave the keyboard & monitor attached, but then you still have "a Model T attached to a PC", and not, like I wanted, a Model T in control of the PC.

There is a way to direct console input/output to the laptop: using the DOS CTTY command. CTTY can redirect I/O to the serial output, for use with any serial terminal, like a Model T. So, issue the command CTTY COM1: on the PC, and set the model 100 to TERM in TELCOM, and there you have it: a C:\-prompt on your model 100, and you are in control of the PC, without keyboard or monitor. Text only, enough for basic file handling, and you better not call up any large listings, but it works.

Solve problem two: Desklink. Once you have started Desklink, how do you get out ? You have to get out because you want to go into CONTROL-mode, to control the flow of files. Sure, press F10 or CTRL-C. But you can't do that, because you have no console at that moment, because your laptop is running TEENY, or FLOPPY, or TS-DOS, ... And when you're out of these programs, Desklink is even less responsive. So the only way to get out of Desklink on a PC without keyboard, is pressing RESET on the PC.

And then you're rebooting, entering the AUTOEXEC again ... Wait ! What if you turned the order around ? I may sound obvious, I may even be stupid, but it took a while before I figured that out: first enter CONTROL-mode, then enter TPDD-mode. And to get back to CONTROL-mode, press reset on the PC, and run TELCOM on the Model T.

Below, we put the above scheme in practice.

Hardware you need:

  • of course, your Model T
  • it has to be a PC with a reset button.
  • a working, crossed serial cable between the two machines, the PC and the Model T

Configure your PC

  • The only limiting factor is the PC's ability to run Desklink. Fastest one I used was a Pentium 75, and that was OK.
  • Configure the PC BIOS in such a way that the machine can boot without monitor, keyboard or mouse attached.
  • Install DOS. Any DOS should do, but don't use Windows. MS-DOS 5.0 is a good choice, because of its enhanced memory management capabilities and small footprint. I've also used PC-DOS 6.3, but my favorite - I want to limit MS-payware - is the free Caldera DR-DOS 7.02. The example files below are written for that version.
  • Install DESKLINK in an new directory C:\PDD2
  • Create a subdirectory C:\PDD2\ROOT


DIRECTORIES

Here is (simplified) tree of my C:-drive. 

  path
  c:\
  +---sd
  +---bat
  +---zip
  +---pdd2
  |   \---root
  \---drdos
      +---ini
      \---tmp
  • Use the following CONFIG.SYS
DEVICE=C:\DRDOS\EMM386.EXE MULTI DPMI=ON FRAME=NONE
DEVICE=C:\DRDOS\DPMS.EXE
DEVICE=C:\DRDOS\SETVER.EXE
SHELL=C:\COMMAND.COM C:\ /E:1024 /P
BREAK=OFF
BUFFERS=15
FILES=20
FCBS=4,4
LASTDRIVE=P
HISTORY=ON,512,ON
COUNTRY=32,,C:\DRDOS\COUNTRY.SYS
DOS=HIGH,UMB

Most of the commands are standard DR-DOS. Line 11 sets the country code (32 for Belgium, use 1 if in the US, or remove the line).

  • Use the following AUTOEXEC.BAT
@ECHO Off
PATH C:\;C:\DRDOS;C:\BAT;C:\SD;..
KEYB BE+
VERIFY ON
PROMPT $P$G
SET TEMP=C:\temp
IF NOT DIREXIST %TEMP% MD %TEMP%
SET DRDOSCFG=C:\DRDOS
NWCACHE 1536 768 /LEND=ON /DELAY=OFF
SUBST E: C:\PDD2
E:
MODE COM1:300,N,8,1
MODE BW40
CTTY COM1:
echo.
echo.
echo.
echo.
echo.
echo.
echo.
echo. +------------------------------------+
echo. ! HD for TRS-80 Model 100, Tandy 102 !
echo. ! using DR-DOS 7.02 and any PC       !
echo. ! Type PDD to emulate a TPDD2        !
echo. ! Press RESET-button to return to    !
echo. ! this menu and take command in DOS  !
cho. +------------------------------------+
pause

Most of it is again standard DR-DOS. I always place my BATch-files in a separate \BAT-folder. SD is StupenDOS (2.0), the smallest file manager I know. Line 3. installs the belgian keyboard-layout. Remove or change as appropriate. In line 10. I define the directory C:\PDD2 as a new drive E:. in the root of E:, is the DESKLINK program. 12. sets the serial port to the correct bausrate. 13. switches the PC to 40 chars/line. 14. switches from video-output to serial-output. If there is no terminal program listening, the batchfile stops there and waits. So, if you have your Model T hooked up, you enter TELCOM, you set STAT to 38n1N, and you enter TERM. Lines 15. to 21 wipe the screen, and 22. to 28. put up a message. Press any key to continue, and you have control of the machine, in DOS.

Attention: while you're installing the PC, it might not be a bad idea to put a PAUSE before MODE BW40. That allows you to break the AUTOEXEC and continue the installation with a normal screen layout.

  • Extra batchfile 1: a must-have

switching to TPPD-mode: PDD.BAT 

@ECHO OFF
ECHO.
ECHO. Press Enter, leave TELCOM and
ECHO. launch your TPDD File-utility.
ECHO.
PAUSE
@ECHO ON
MODE BW80
CTTY CON:
MODE COM1:19200,n,8,1
E:
CD \ROOT
DIR > DIR.DO
CD \
DESKLINK

Lines 1 to 6 tell you what to do. Remember, on the Model T, you're still in TELCOM. Line 8. is for when someone is watching the PC's screen - in case one is attached. Desklink doesn't look good when launched on a 25x40 screen. Line 9. puts the computer back in normal console mode. Line 10. puts the serial port in high gear. Line 11 switches to the substituted drive E:, line 12 goes into \ROOT and line 13 dumps the directory to a DIR.DO file. In case you forgot to look at the files, you can still load them into your Model T to look at the directory as a simple text-file. Line 14 and 15 come back to the root and start Desklink. By then, you should be out of TELCOM and into TEENY.

Save in C:\BAT.

  • Extra batchfile 2:

If you ever have started your PC and stopped the autoexec to work on the PC, it might be in a weird state. You can also executee this batch-file if you want to release your PC from CONTROL-mode. 

@ECHO OFF
ECHO.
ECHO. Resets console to standard display and
ECHO. keyboard and to 25 lines by 80 chars.
ECHO.
@ECHO ON
MODE BW80
CTTY CON:

Save in C:\BAT.

Configure your Model T.

  • Install a DOS/disk-client. That's all. I've used TEENY all the time, though I would prefer FLOPPY for the TPDD2. I did consider DSKMGR not stable enough, maybe because of an incompatibility between it and Desklink? Of course, you could use any DOS in ROM. I have no ROMware. Anyway: the setup I'm describing is NOT auto-configuring/loading the DOS-client, so that has to be done before. You can use the PC for that purpose, but it will have to be fully independant.


In practice

  • hook up the Model T and the PC with the serial cable
  • turn on the PC
  • turn on the Model T
  • enter TELCOM, set STAT to 38N1N, and enter TERM
  • on screen you'll see:
 +------------------------------------+
 ! HD for TRS-80 Model 100, Tandy 102 !
 ! using DR-DOS 7.02 and any PC       !
 ! Type PDD to emulate a TPDD2        !
 ! Press RESET-button to return to    !
 ! this menu and take command in DOS  !
 +------------------------------------+
 Press any key to continue
  • press any key, and you get a DOS-prompt C:\. Remember MS-DOS? You can access floppydrive A:, and copy files to and from C:\PDD2\ROOT or E:\ROOT (same place)
  • start TPDD emulation with DESKLINK by executing PDD.BAT: you're now in TPDD-mode
  • get out of TELCOM, and use your Model T with the DOS/disk-client of your choice.
  • If you want to leave TPDD-mode you have to press the reset-button on your PC.
  • If you want to stop: simply turn off the machine. (may not be a good idea when using an XT where you have to 'park' your HD..)
  • You can also get out of CONTROL-mode by using RTTY.BAT, and then turn off the PC.

Credits

  • Richard Hanson, the keeper of Club-100
  • the original author of Desklink
  • all the people on the M100 mailing list
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