rtd DM5816, User Manual

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DM5816/DM6816 RTD Embedded Technologies, Inc.
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Before exiting your program, you must restore the interrupt mask register and interrupt vectors
to the state they were in when your program started. To restore the IMR, write the value that
was saved when your program started to I/O port 21H. Restore the interrupt vector that was
saved at startup with either DOS function 35H (get interrupt vector), or use the library routine
supplied with your compiler. Performing these two steps will guarantee that the interrupt status of
your computer is the same after running your program as it was before your program started
running.
Common Interrupt Mistakes
•
Remember that hardware interrupts are numbered 8 through 15, even though the
corresponding IRQs are numbered 0 through 7.
•
Two of the most common mistakes when writing an ISR are forgetting to clear the
interrupt status of the DM5816 and forgetting to issue the EOI command to the 8259
interrupt controller before exiting the ISR.