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8. I/O Device Hacks > 78. Rewire Your COM Ports

Rewire Your COM Ports

Rewire an old COM port board to use available IRQs to run four ports simultaneously.

In this hack, we’ll rewire the IRQ lines of an old 8-bit COM port card to configure COM3 and COM4 ports to use IRQs 5 and 7. Rewiring older I/O cards takes a bit of skill—specifically with hand tools and a soldering iron.

Figure 8-3 shows an obvious rewire of IRQ signals. Accomplishing this rewiring required opening the circuit traces from the IRQ 3 and 4 connection “fingers,” then adding wires from the IRQ 5 and 7 “fingers” to the circuit traces that once connected to IRQs 3 and 4.

IRQ lines rewired on a COM port I/O card
Figure 8-3. IRQ lines rewired on a COM port I/O card

If you decide to try this at home, you need to know the connector pin information to locate the respective IRQ circuit traces, which are:


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