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| From: Marko_Mäkelä
Date: 2000-08-15
Subject: Re: Interrupts again
|
On Tue, 15 Aug 2000, Zsolt Prievara wrote:
> Hey, nobody knows the interrupts? Or where can I find info about it?
On the plus/4 processor, there are two level-sensitive interrupt inputs:
-RESET and -IRQ. The falling-edge-sensitive -NMI input is not wired to the case of the chip, so you cannot use it. When e.g. the TED causes an interrupt, it pulls the -IRQ line low. The processor will eventually start the 7-cycle-long IRQ sequence if it detects that -IRQ is low and that the I flag is clear. The IRQ sequence sets the I flag, so the processor won't keep executing that sequence all the time. When the program clears the I flag (with CLI or RTI), the interrupt sequence will start again, unless the IRQ line was pulled high again (this is why the interrupt source should be acknowledged in the interrupte handler).
I hope that this answered your questions.
Marko
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