RS232.1

Hello All
  Not all serial cards are alike. We have found out that there are some
cards that want to support IRQ3 and IRQ4 so badly that even the gold
fingers for the other IRQ lines are MISSING. To make it easy for you,
make sure if you can, that you buy a com board that has all the fingers
on both sides.
  If you have one that doesnt, all is not lost. After talking to technicians
and Mike WA8BXN, there is another way.
  Here it is:

You can use same IRQ lines (share them amoungst devices) as long as:
1) They have different addresses
2) You modify the com board by placing a diode in series with the IRQ
   line.

Theory:
   For example, if you run com1 on 3F8 IRQ4 and want to run com3
on 3e8 IRQ4, this is what happens.
   Under no Interrupt requests, the com board keeps the IRQ4 line
of the pc buss socket LOW.
   If com1 gets the interrupt, it tries to raise the IRQ4 line high,
but since you have another com board that is on com3 with the same
IRQ line (which it is holding low since it has no interrupt), the
IRQ from com1 will never be seen.
   You must isolate both IRQ lines via cutting the traces leading
to the IRQ4 line on BOTH com boards and inserting a diode in series
with the foilcut in both boards. The positive end of the diode points
in towards the com board and the cathode points towards the pc buss.

Here is a list of pin connections. Pick what ever pin is applicable to
your computer as per free IRQ lines you may wish to use.


Pin: IRQ:
---- ----
B4 2
B25 3
B24 4
B23 5
B22     6
B21 7

The B side of the connector is the FOIL or BOTTOM of the 2port com board.
The A side has the components on it.
CONTINUED IN FILE RS232.2