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From: "petrus bitbyter"
Subject: Re: ISA IRQ signal active how long?
X-Newsreader: Microsoft Outlook Express 5.50.4807.1700
Date: Fri, 04 Oct 2002 11:02:12 GMT
NNTP-Posting-Date: Fri, 04 Oct 2002 13:02:12 MET DST
Organization: chello broadband
1. The only way to do it right is using a tri-state driver. This makes it
possible to select an required IRQ-line and de-activate the lines you do not
use but that may be used by others. A printer port for instance uses its
/ACK-line to interrupt the processor. It is buffered by a tri-state buffer
so you can select the IRQ-line you want to use (traditionaly IRQ5 or IRQ7)
or deselect them all. (Which is often done as most printers do not need
2. According to the ISA-bus specification the IRQ-signal should be asserted
until it is switched off by the interrupt service routine.
3. Also according to the ISA-spec the IRQ-controller is set to edge
triggering. Nevertheless point 2 is also required.
Succes with your development.
"Ru-Chin Tsai" schreef in bericht
> I design a ISA card with IRQ support. We know 8259's IRQ signal is
> active high. I have read many posts about ISA IRQ pin and remain
> feeling some confusions. Please help me solve these problems.
> 1. The ISA IRQ will be totem-pole or open-collector or tr-state output
> It seem to have no standard about this issue. Many answers were
> posted on
> newsgroup and I can't identify which one is correct output
> 2. When ISA card request interrupt. It must assert the IRQ signal. But
> how long
> does IRQ signal be asserted(active high)?
> 3. Should I care the 8259 PIC act as edge-trigger or level-sensitive
> Thank you for your help sincerely. These problem delay my project for
> long time.
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