





                    USE TANDY 1000 16 COLORS MODE ON A PCJR

                    (Modified on 12-22-1988 by A. Martins)


This mode will allow the use of Tandy 1000 16 color mode on a PCjr.  I found
I can run Flight Simulator 3 using the Tandy 1000 option.  Other programs
that now work are Deluxe Paint 2, Deskmate Software, etc.  In general, any
program which exhibits horizontal black stripes before this mode will now
run properly.


                                 ͻ
                                                          
                                        14           8    
                                       Ŀ     74S86 Piggy
                                       ÿ 74S86 on         Backed on top
                                        74LS04 ZM33      of 74LS04.
  ͼ           Pins 7 & 14
                                        1 2 3        7      attached. All
                                          ͼ  others lifted.
                       ͼ ͻ       Pins 1, 2, 3 of
                                                           74S86 are wired
     16            9        20                11           as shown.
    Ŀ     Ŀ    
    ÿ                    ÿ                      
       74LS157 ZM31           74LS273 ZM30    
             
     1 2 3 4 5 6 7 8        1 2 3 4 5 6 7 8 9 10         Double lines are
  ͹                                   ͼ     added wires.
         ͼ                                  Single lines are
        //             existed traces.
                          ^
                           cut this trace here



         40                                     21
        Ŀ
                                                 
                                                 
        ÿ                                        
                    8255A Chip  ZM22            
                                                 
                                                 
        
         1                                      20




Steps:  1. Cut trace from pin 2 74LS157 (ZM31) to pin 9 74LS273 (ZM30)

        2. Piggy Back a 74S86 onto (ZM33) 74LS04.  Pins 7 & 14 are the only
           2 that need to be soldered to the 74LS04.  All other pins on the
           74S86 should be lifted level so as not to touch the 74LS04.
           BE SURE TO PROPERLY ALIGN THE CHIPS PIN TO PIN...
           THAT IS PIN 1 TO 1, etc...

        3. Add the 3 wires shown in the diagram above:
            a) pin 3 of 74LS157 to pin 1 of 74S86
            b) pin 9 of 74LS273 to pin 2 of 74S86
            c) pin 2 of 74LS157 to pin 3 of 74S86

        4. Use a 32K video buffer.  Specify either Pcjrmem /c or /e.
           If you use Jrconfig, use the v32 switch and s1.

        5. Hint: When adding the wires, solder to the chip legs, not the board
           traces.  It is much easier to add/remove if this technique is used.

                           Good Luck... Tony Cooper

                     =-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=

    The above is unchanged, exactly as Mr. Cooper wrote it and as I got it
from Compuserve recently, except for the 2 first lines which were added by me.
The following, is also of my doing.

    I have found that the use of the v32 and s1 switches, when using
Jrconfig, is necessary only with some games.

    I have installed the chip (costs less than $2.00) on my Jr and so far have
tried 5 programs that did not run in 16 colors before. Leisure Suit Larry II,
was one of them.  Now it runs in 16 colors instead of 4. I know that it says
"Can't run on a PCjr!", but if you have PC Enterprises' Configuration
Cartridge, and you switch to PC mode, it will run. However, if you chose Tandy
mode you would get those lines or dots on the screen as you probably have seen
already.  Chosing CGA would work in 4 colors only. After I installed the chip
as described above, everything worked fine in TANDY mode.
    But because I don't know if there are programs that may not like this
mode, I added a switch to the above so I can either have the Tandy mode or
completely disconnect the chip, putting the Jr exactly as before I did this
change; all I have to do is to push the switch up or down. Maybe it is not
necessary but I did it just in case. I did not yet had the need to switch back
to PCjr mode to run a program, so far.
    For those that may want to have the switch, I include the following
diagram. It is the same as the above except that it incorporates the switch.



                                      14           8    74S86 Piggy Backed
      Double lines are               Ŀ   on top of 74LS04.
      added wires.                   ÿ 74S86 on       Pins 7 & 14 attached.
      Single lines are                74LS04 ZM33    All others lifted.
      existed traces.                   Pins 1,2,3 of 74S86
                                      1 2 3        7    are wired as shown.
                                        
                                        ͻ
                                      ͺͺͻ
                                        ͻ          
                                                                
   16            9         20                11                 
   Ŀ      Ŀ                
   ÿ                     ÿ                                  
      74LS157 ZM31            74LS273 ZM30                
             ĺĺĺĿ TANDY
    1 2 3 4 5 6 7 8         1 2 3 4 5 6 7 8 9 10     o /   o /   o / mode
      ĺ//Ĵ         /     /     / 
                     ^                    o     oͻ  oͻ
                                                                  
                      cut this trace here      oo    o     PCjr
                                                  ĺ   mode
       ͺͼ
      ͼ
                                                          SWITCH

         40                                     21
        Ŀ
                                                 
                                                 
        ÿ                                        
                    8255A  Chip  ZM22           
                                                 
                                                 
        
         1                                     20

        This is a big chip, easy to find, that will help you to locate
        the other three. They are all under the disk drive.


    A good location to put the switch is next to the plugs for the joy sticks.
You have to drill a 1/4 in. hole just below the vertical openings at the back
of the Jr. One 3 PDT toggle switch, Catalog No. 275-661 from Radio Shack, does
the job well.
    It is great to be able to run all those programs that used to run only on
the TANDY. It really works.


                                                      A. Martins                                                                                                                                                                                                                                                                                          