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From: Jean-Michel Friedt
Subject: Re: ISA IRQ signal active how long?
Date: Fri, 04 Oct 2002 12:00:11 +0200
Organization: IMEC Belgium, http://www.imec.be
NNTP-Posting-Date: Fri, 4 Oct 2002 10:00:13 +0000 (UTC)
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> 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
I don't have the specs of ISA with me but all the designs I have made
triggered the IRQ pin by going from Hi-Z (with pull down IIRC) to hi
down to a single ISA cycle duration and I never found any problem with
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