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The Interrupter generates an interrupt at one of the seven VMEbus interrupt levels. The interrupt level is selected by jumper JB1. When the VMEbus interrupt handler for this level acknowledges this interrupt, the interrupter (CC175) will generate a Status/ID byte, negate the interrupt line (ROAK - Release on Acknowledge) and responds with DTACK. The Status/ID byte is retrieved from the Module ID register.
Figure 5-4 Status/ID Byte Register
When the CC175 wants to place a VMEbus interrupt, it should first check that there is no interrupt pending by reading the Interrupt Control Register (ICR) and checking that the ENIRQ bit is '0'. Then the ICR is written with the ENIRQ bit '1'. Writing a '1' to the ENIRQ bit will actually assert the VMEbus interrupt line. As long as the interrupt is not acknowledged by the VMEbus master, the ENIRQ bit will read as '1'. After a corresponding interrupt acknowledge cycle has been generated on the VMEbus, the ENIRQ bit will be cleared ('0).
Figure 5-5 Interrupt Control Register
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