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MRT
Account closed
Registered: Sep 2005
Posts: 149 |
2 bit irq loader
Hmm, just a question...
Is there a 2 bit irq loader, which doesn't require blocking other interrupts while loading a byte?
i.o.w. Is there a realy fast irq loader which doesn't block any interrupts and let me use my beloved sprites? :-)
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chatGPZ
Registered: Dec 2001
Posts: 11386 |
what about programming ATN as output, but still using it as input? works with certain other i/o lines atleast :) |
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Krill
Registered: Apr 2002
Posts: 2980 |
I don't think that would work. If you check with the 1541's bus circuitry, the ATN line is heavily interlocked with the data line, and there is some blocking diode in the 1541->C64 direction, iirc. I second JackAsser there, C64->1541 works, but not the other way around. |
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chatGPZ
Registered: Dec 2001
Posts: 11386 |
ah yes, i remember now :) |
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MRT
Account closed
Registered: Sep 2005
Posts: 149 |
Ehr... silly question maybe. But I'm writing my own loader now and I was wondering why the VIA reg and the CIA reg both have input and output bits.
Wouldn't it be more logical if you would just have a data bit and a clock bit, which would reflect the current state?
What is the benefit of having the in/out bits per line?
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Graham
Account closed
Registered: Dec 2002
Posts: 990 |
The benefit is that you don't need to switch the data direction all the time. |
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MRT
Account closed
Registered: Sep 2005
Posts: 149 |
Hmm, but do you need to clear it?
ie. when I set the data-out from low to high, will the data-in automatically be high too?
Or will the data-in remain the same until the other party lowers it?
And if so, can I reset it too? by clearing the via1 for example?
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MagerValp
Registered: Dec 2001
Posts: 1078 |
CLK/DATA IN is active when the output is active on either the computer or one of the drives. If all are inactive, CLK/DATA IN is inactive.
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MRT
Account closed
Registered: Sep 2005
Posts: 149 |
ehr... yeah, but on the VIA1 register... When I set data-out to active, will then automatically the data-in on that same VIA1 register be set to active?
Edit: Or will the data-in on that VIA1 register only be set to active, when the C64 (or another drive) sets that line to active? |
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Krill
Registered: Apr 2002
Posts: 2980 |
Why don't you just check it yourself? Doesn't take long to code, really. :) |
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Krill
Registered: Apr 2002
Posts: 2980 |
Oh, and btw., i have an idea on how to make the 2bit+atn protocol work with multiple drives connected (and turned on). Will implement that some day.. |
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