G.ABRAMS@SU-SCORE.ARPA (Info-Atari Moderator) (08/28/86)
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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
-------