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INT and DMA switches

Putting the INT (interrupt) switch to its inactive position (down) causes the EXT-BUS line IRQ (interrupt request) not to reach the intended destination, thus having external interrupts unavailable.

In systems making use of external interrupts, the INT switch must remain active (up) all the time. However, you may want to flip it down for testing purposes.

This also apply to the DMA switch with respect to the EXT-BUS line BRQ (bus request). In systems making use of DMA, this switch must remain in active position (up) all the time except for testing purposes.