MS400

Shared Interrupt Modification
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Purpose:
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This modification will allow a packet BBS using the CBBS, the W0RLI, the
KA2BQE, or WA7MBL V3.x code to install 4 ports using only one slot and
one interrupt request line (IRQ) on an IBM PC or compatible.  The change
is nondestructive since no traces are cut and can be easily removed.

Hardware:
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The DFI MS-400 board provides 4 ASYNC ports and is available from
several sources.  It comes in two flavors: XT and AT with the only
difference being the 8250 versus the 16450 chips.  As shipped from the
factory, the MS-400 requires one IRQ line per port.

Additional parts required are 4 small signal diodes (I used 1N914s
from Radio Shack) and a 4.7K resistor (1/8 or 1/4 watt).

JDR MicroDevices carries (or at least did so on Nov 1st, 1987) the
MS-400.  Their part number for the XT version is MCT-MS and it was priced
at $80.  Address: 110 Knowles Drive, Los Gatos, CA 95030.  Their phone
is (800)-538-5000 or (408)-866-6200 (for CA and non-US).
CONTINUED IN FILE MS400.4