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From: faiman@uiucdcsb.cs.uiuc.edu
Newsgroups: comp.sys.misc
Subject: Re: Interrupts on the N* Advantage
Message-ID: <166200001@uiucdcsb>
Date: Sat, 6-Dec-86 11:05:00 EST
Article-I.D.: uiucdcsb.166200001
Posted: Sat Dec  6 11:05:00 1986
Date-Received: Sun, 7-Dec-86 20:55:14 EST
References: <1084@brl-adm.ARPA>
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Nf-ID: #R:brl-adm.ARPA:-108400:uiucdcsb:166200001:000:1111
Nf-From: uiucdcsb.cs.uiuc.edu!faiman    Dec  6 10:05:00 1986


    There are two issues here.  One is how the Z80 handles interrupts and, as
David Drexler points out, any decent Z80 manual or assembly language reference
will tell you that.  The other is how the rest of the Advantage hardware
interacts with the interrupt system, and for this you need the Advantage
Technical Manual.

    Since we used to have a lab with Northstars here at Illinois, I can give
you a few pointers, but let me warn you that I'm speaking from memory, so that
you should be careful to check the details.  First, the Z80 provides three
interrupt modes:  IM0 (default) gives 8080 (remember the?) compatibility;
IM1 causes an automatic RST 38H on interrupt; and IM2 provides true vectoring,
taking the low address byte from the device and the high from the I register.
Now -- and here my memory is hazy -- I believe that the Advantage provides
no direct way of placing an RST or vector on the data bus, so that you have to
use IM1.  But, you'd best check the manual.  I also remember that the manual
was not very clear on this point.  If Northstar is still in business, why not
give them a call?