Ask anything your want about Megadrive/Genesis programming.
Moderator: BigEvilCorporation
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mickagame
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by mickagame » Thu Oct 16, 2014 8:57 am
Reading adress range cause machine lock-up.
What happen exactly when it happen?
Are there signals concerned in this mecanism?
Are thé CPU halten?
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HardWareMan
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by HardWareMan » Thu Oct 16, 2014 11:52 am
Use search engine.
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KanedaFr
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by KanedaFr » Thu Oct 16, 2014 12:13 pm
did you look at charles doc, etc... ?
Some addresses are invalid and if you check z80's one you need to request its bus first
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Mask of Destiny
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by Mask of Destiny » Thu Oct 16, 2014 8:36 pm
A lock up is typically a symptom of nothing bringing /DTACK low for a memory request. The 68000 has an asynchronous memory interface which means that it waits to complete a bus cycle until something tells it that the operation is complete. If /DTACK never goes low, the bus cycle lasts forever.
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mickagame
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by mickagame » Fri Oct 17, 2014 5:58 am
Thanks it's exactly what i want to know
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l_oliveira
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by l_oliveira » Tue Dec 30, 2014 5:56 am
An computer built around 68000 CPU would have a counter and logic circuit to trigger an BUS ERROR exception using the /BERR (Bus Error) pin on the CPU after a set number of machine cycles without /DTACK pulse. MD doesn't have that because was built with cost saving in mind.