PRT187.DOC

Tandy 200 Port 187

The Tandy 200 uses three input lines that are easily accessed.  The printer
port BUSY (pin 21), the printer port NOT BUSY (pin 25), and the bar code
port RX DATA (pin 2) can be tested easily by the BASIC INP(X) function for
a HIGH or LOW condition (all are normally HIGH).  By using all of the
possible combinations of these data lines, eight discrete combinations are
found.  These combinations are in the following table with the results of
the  function:

  V=INP(187).

BAR RXD  BUSY  NOT BUSY = VALUE
   0      X      X      =  241
   0      X      0      =  243
   0      0      X      =  245
   0      0      0      =  247
   X      X      X      =  249
   X      X      0      =  251
   X      0      X      =  253
   X      0      0      =  255

    0=OPEN   X=GROUNDED


The BASIC program PRT187.200 will run on the T200 and display the status of
the lines.  I do not know if the data lines are exactly the same on the
Model 100/102 as I do not currently have access to one for testing.  This
program shows the branching that is possible with the different combinations
of lines pulled LOW.  This is a simple way to use the T200 for external
event driven programming.  Hook it up to something imaginative and useful
like a wind direction indicator or a burglar alarm with three zones.


The pins on the Centronics (printer) end of the printer cable that
correspond to the T200 pins are as follows:

   T200           =    Centronics 36 Pin
---------------------------------------
BUSY (pin 21)     =    BUSY (pin 11)
NOT BUSY (pin 25) =  NOT BUSY (pin 13)


Have fun with this and good luck.

Paul R. Jorgenson  KE7HR
70416,460
28 November 1992