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Newsgroups: comp.sys.apple2.comm Path: blue.weeg.uiowa.edu!news.uiowa.edu!uunet!news.mathworks.com!udel!gatech!psuvax1!news.ecn.bgu.edu!newspump.wustl.edu!news.starnet.net!wupost!waikato!comp.vuw.ac.nz!actrix.gen.nz!dempson From: dempson@atlantis.actrix.gen.nz (David Empson) Subject: Re: Still having problems... Message-ID: <D30HvI.4tE@actrix.gen.nz> Sender: news@actrix.gen.nz (News Administrator) Organization: Actrix - New Zealand Internet Service Providers Date: Thu, 26 Jan 1995 12:11:40 GMT References: <D2rz3z.EEH@sue.cc.uregina.ca> <D2t09q.BIM@actrix.gen.nz> <D2xIE4.BnD@sue.cc.uregina.ca> X-Nntp-Posting-Host: atlantis.actrix.gen.nz Lines: 61 In article <D2xIE4.BnD@sue.cc.uregina.ca>, charles macdonald <macdon@HERCULES.CS.UREGINA.CA> wrote: > > The problem was a Time][ card installed in slot#7 (given to me about > 9 years ago). It was wreaking havoc with the interrupts. Aha! Easy solution there: change the switches on the Time ][ so that it doesn't have any interrupts enabled. (It shouldn't have, unless you have written some software to use them.) I see from a later posting that you don't have a manual. Luckily, I do. There are eight switches on the card. To disable all interrupts, set all the switches to the OFF or OPEN position (towards the edge of the board). In case you ever want to use the interrupts, the switches operate as follows: 1 1 Hour NMI 2 1 Minute NMI 3 1 Second NMI 4 1024 Hz NMI 5 1 Hour IRQ 6 1 Minute IRQ 7 1 Second IRQ 8 1024 Hz IRQ NMI and IRQ refer to the Non Maskable Interrupt and Interrupt ReQuest signals. Only one of the four interrupts in each group may be enabled. The 1 hour, 1 minute and 1 second interrupts generate a pulse of 122.1 millisecond duration on the appropriate interrupt line. The 1024 Hz interrupt generates a pulse of 488 microseconds every 976 microseconds. It is a very bad idea to have NMI enabled, because an NMI can occur at any time, even while the processor has interrupts disabled. The worst example of this is during a disk write operation: an NMI can cause part of the disk's contents to be destroyed! The IRQ is less dangerous. If the processor has interrupts enabled, an IRQ from the card will cause the interrupt handler to be called immediately (you can install up to four interrupt handlers if you are running ProDOS). It is normal practice for an interrupt handler to check that the interrupt comes from its device. This is a little difficult to do with the Time ][ card, but not impossible. If no interrupt handler has been installed for the Time ][, an interrupt from the card will immediately crash the computer (as you have discovered). Interrupts are normally disabled (within the processor) until you run a communications program or boot ProDOS-8 1.2 or later. -- David Empson dempson@actrix.gen.nz Snail mail: P.O. Box 27-103, Wellington, New Zealand