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80C186EC/80C188EC Microprocessor User's Manual

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INTERRUPT CONTROL UNIT<br />

Timer 0<br />

Highest Priority<br />

Timer 1<br />

DMA Channel 2<br />

DMA Channel 3<br />

Timer 2<br />

Serial Channel 0 Receive<br />

Serial Channel 0 Transmit<br />

INT7 Pin<br />

Lowest Priority<br />

A1231-0A<br />

Figure 8-22. Default Slave 8259 Module Priority<br />

8.5.1.2 Indirectly Supported Internal Interrupt Sources<br />

The interrupt request lines for DMA channel 0 and DMA channel 1 and the receive and transmit<br />

interrupts for serial channel 1 are not tied internally to the Interrupt Control Unit. These interrupt<br />

requests are routed to external device pins through the Port 3 multiplexer (Figure 8-23). If a system<br />

requires interrupt support for these devices, the multiplexed interrupt request outputs must<br />

be externally connected to the INT input pins of the Interrupt Control Unit.<br />

8-38

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