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  at 03:42:54 CDT
Date: Wed, 27 Aug 86 10:42:23 SET
To:  info-atari16-request@su-score.ARPA
From:  FGCBA10%BLEKUL11.BITNET@WISCVM.WISC.EDU
Subject: re: 520ST parallel printer port doubles characters?

DEER JAN,

THE PROBLEM OF THE DDOOUUBBLLEEDD CHARACTERS LIES IN THE STROBE
PIN NUMBER 1 THAT GOES TO THE PRINTER.  THE PULSE IS TO LONG SO
AFTER THAT THE BUSY-LINE HAS DROPPED THERE IS STILL A STROBE PULSE
AND THE CHARACTER WILL BE PRINTED AGAIN.
______
STROBE ---------I                 I---------------
                I                 I
                I-----------------I

                 I------------I
                 I            I
BUSY-------------I            I-------------------

INTERUPT THE STROBE LINE AND PUT THE FOLLOWING SCHEME BETWEEN IT
THEN THE PROBLEM HAS TO BE SOLVED.


          I +5V
          I
          R = 10K
          I
          I   2.2NF
          I--II--I
  +5VI    I      I
     I    I      I
 I---.----.------.-----.----.----.----.----.----I
 I  16                                     9    I
 I                 74LS123                      I
 I   1                                     8    I
 I---.----.------.-----.----.----.----.----.----I
     I    I      I     I                   I
     I    I------I     I                   I
     I           I     I                   I
     I          +5V    I                 -----
     R = 100           I                  GND
     I                 I
     I                 I
     I                 I
  STROBE IN        STROBE OUT
FROM COMPUTER      TO PRINTER








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