3.2.3 Interrupt Capability

Each group on the BI-0433 can generate an interrupt request, independent of the other groups. Possible sources for interrupts are the digital Input signal, the index signal, the 32 bit counter carry and borrow signals and the fault detection circuit signals.

A Compare State Register is implemented on the BI-0433 to detect events on the digital Input signal and the index signal. The next figure shows how this circuit is functionally implemented.

Figure 3-4 Compare State Circuit

Several registers are implemented on the BI-0433 for generating and controlling of the interrupt capability. Each channel has the following interrupt control/status registers:

To detect a change in the input lines, the comparator must compare the real time input lines with a copy of the previous state of the input lines. A copy is made of the current state of the input lines by reading the Direct Input Register, and this data should be written into the Compare State Register. An interrupt will be generated as soon as the real time input changes and the corresponding input is enabled in the Interrupt Mask Register. The current states of the index and digital Input signals are saved in the State On Interrupt Register register at the time of the interrupt request. Each group has its own interrupt request signal to the Bus Interrupter Module.

Further detailed programming considerations are given in chapter 5.