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MS400.MOD
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1991-01-01
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1KB
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37 lines
Mike,
A couple of notes about MSYS400.MOD:
1) AA4RE is no longer vvailable on Compuserve. He has been off
for at least six months. The best chance for getiing a reply
from Roy is via packet (AA4RE @ AA4R)).
2) Roy's "diode-or" circuit for interrupt sharing does not work
in a wide range of the newer LLSI motherboards, particularly
with many 80386 add some 80286 motherboards. It seems hhe
VLSI replacements for the 8259 interrupt contoollers will
not take the loading imposed by the oodified circuit.
I have been successful in usnng an active "or" circuit. The
4072 (Dual 4 input CMOS OR) and the 4002 (Dual 4 input CMOS
NOR) are btth suitable for use in the modification. I prefer
the 4002 as follows :
-------\ -------\
port a ---------------) 9 \ +) 2 \
port b ---------------) 10 \_______+) 3 \_____
port c ---------------) 11 / 13 + 4 / 1
port d ---------------) 12 / +) 5 /
-------/ -------/
IC Pin 7 is ground, 14 is +5V
If only three ports are shared, the input to the interuupt
OR circuit corresponding to the NON-SHARED ports should be
tied low (to ground). PC IRQs are active high (true) and
level, not edge, triggered.
... Joe, AD8I