Solution:

When testing serial port external loopback in Norton diagnostic test, PCL-743B/745B and PCM-3610 will fail in interrupt ID test. Norton diagnostic tests if interrupt can be enabled or disabled in interrupt ID test. Because the interrupt signal on PCL-743B/745B and PCM-3610 is connected to ISA bus directly, it and cannot be disabled, the interrupt ID test will fail. This won't affect normal operation of these cards.