Tandy  1000 SX  (250-1051)         Settings            Faxback Doc. # 1182

Note: Refer to Faxback Doc. # 1250 for Main Logic Board Layout.

Below are main logic board jumper and switch settings:

E1-E2     Selects 384K RAM (standard)
          (remove to select 640K)
E3-E4     Indicates NO coprocessor chip installed
          (remove to enable coprocessor)
E5-E6     Connects printer select signal to parallel port
          (remove to disable printer select signal)

Switch S-2:

     #1   OFF     Selects composite monochrome monitor
          ON      Selects color RGB monitor      (standard)
     #2   OFF     Disables on board interrupt 5
          ON      Enables on board interrupt 5   (standard)
     #3   OFF     Disables on board interrupt 6
          ON      Enables on board interrupt 6   (standard)
     #4   OFF     Disables on board interrupt 7
          ON      Enables on board interrupt 7   (standard)


The Tandy 1000 SX Computer (250-1051) is an 8 Bit, XT Class computer that
utilizes an 8088 processor.  The machine was originally marketed in 1986
for about $ 800, and was designed as a direct competitor to the original
IBM PC/XT and the other XT class IBM "Clone" computers that were being sold
at that time.

If you are needing a replacement for the original software or the original
owners manuals that came with this computer, you can also order them from
the Tandy RSU department at the telephone number listed above. The original
software consists of the diskettes listed below:


The MS-DOS disk will allow you to boot up the computer, format disks, etc.
The DeskMate program includes a simple word processor, spreadsheet, and
other applications.

The Tandy 1000 SX originally only came with 384K of RAM.  While this was
enough for the original software and many of the programs that were on the
market at that time, it is hardly sufficient to run most of the programs
out on the market today.  While the computer can be upgraded to 640K of
RAM memory by adding a memory upgrade kit (RSU# 11492584, $ 39.99) this
still would not be enough for most of the software that is currently avail-

In addition, the 1000 SX utilizes an 8 Bit processor, the 8088.  To run
many of today's software packages, you must have at least a 16 Bit 80286
processor.  Just as there is no way to turn a 4 cylinder engine into an 8
cylinder engine, there is no way to make an 8 Bit computer into a 16 or 32
Bit computer, regardless of the make and model.

When shopping for software, you should keep in mind the amount of memory
you have and whether or not you have a hard drive.  Most software will
state clearly on the outside of the package how much memory they require
and whether or not they require a hard drive.  Other specifications which
are generally mentioned in requirements is type of monitor you have and
what processor is used in the computer.  The built in video is CGA, and,
as stated earlier, you have an 8088 processor.

We also suggest that you contact one of the mail order companies listed
below when looking for software and upgrades.  Both of these companies
specialize in software and peripherals and upgrades for older XT class
computers, such as the 1000 SX.

PC ENTERPRISES                        DCS INDUSTRIES
WALL  NJ  07719                       ATHENS  OH  45701
800-922-7257                          800-537-3539
908-280-0025                          614-592-4239

Please note that the above mentioned companies are not affiliated with
Tandy Corporation / Radio Shack in any way.  Therefore, we cannot guaran-
tee nor support the use of their products.

Because of this, we feel that we must advise you that if you wish to use
most of the software on the market today, and wish to go "online", you
would probably be better off saving up for a new computer, rather than
sinking a large amount of money into your older computer.  However, if this
is not specifically a requirement, and you are simply interested in simple
word processing and filing, the 1000 SX should be able to provide useful,
if somewhat limited service.

Mouse Driver:

The mouse driver needs to be installed while the computer is in the slow
mode (8080 processor mode).  There are several ways to accomplish this.
In the config.sys if the mouse.sys driver is listed before the express.sys
driver this will be one simple solution.  Also, if the "88" and "CPU"
parameters are used with express.sys and mouse.com is placed in the auto-
exec.bat file, hot keys will appear at the bottom of the screen to allow
you to manually switch between the two processors.  A third way to make
the two work together would be to in your autoexec.bat file use the
pct 88 command to switch to the slower speed followed by the mouse.com and
the pct 286 to load mouse then switch it back to the faster mode again.

Function  Keys

The following is a list of the function keys on old 1000s (1000/A/SX/TX):

F1 = Mono Mode
F2 = TV Mode
F3 = Swap Drives
F4 = Low Speed

The keys will not do anything on machines that do not support that function
(ie. the original 1000 is a 4.77 MHz machine only, so Low Speed will not do

To use the keys, you must hold down the appropriate key while powering up
the machine.

Or you can use the DOS MODE command to toggle TV/Mono/Low Speed modes (ie.
MODE SLOW to switch to slow mode). This feature works on the Tandy 3000
DOS as well.

I/O Port Error Message - 378H:

The error message you are encountering with your system is due to the printer cable that is connected to the parallel printer
interface on the computer end of the cable is upside-down.  We recommend you turn your system off, disconnect the cable, turn it over so
the side that shows "top" is facing up, plug it back in, and then turn power back on.

3.5" High-Density Floppy Disks

Tandy Corporation/Radio Shack does not support installing a high density
drive in your Tandy 1000SX computer as the on-board Floppy Drive Controller
(FDC) circuitry is not designed to work with this type of drive.  The FDC
circuitry only has the capability of recognizing a low density disk drive.

The DMA channel assignment is as follows:

        Channel 0         Refresh
        Channel 1         Optional SDLC/FDC2
        Channel 2         Floppy Disk 1
        Channel 3         Optional Hard Disk

As well, the main logic board of the Tandy 1000SX system has dipswitches
that are used as follows:

        Switch position 1  ON        Selects color RGB
                           OFF       Selects composite monochrome
        Switch position 2  ON        Enables IRQ5 (Vertical sync)
                           OFF       Disables IRQ5
        Switch position 3  ON        Enables IRQ6 (Floppy Disk)
                           OFF       Disables IRQ6
        Switch position 4  ON        Enables IRQ7 (Printer)
                           OFF       Disables IRQ7

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