Questions tagged [dma]

Direct Memory Access in historical computers and the history of DMA itself. DMA allows peripherals to access memory directly without using the main processor.

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How does the VIC-II/CPU memory access work on the C64?

As a programmer I knew that on the C64 the CPU got the bus in the high phase of PHI2 and the VIC-II got it in the low phase and also stole extra high phases when required. However, it wasn't until ...
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2 votes
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Does C64 /DMA assertion immediately disconnect the CPU from the address bus?

I have heard several claims (in the comments on this question and answers) that asserting the D̅M̅A̅ signal on the Commodore C64 cartridge port will immediately take the CPU off the bus by deasserting ...
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Apple II DMA daisy chain also used to arbitrate /INH?

On the Apple II series of computers, peripheral cards contend for bus mastership through a priority daisy-chain system. A peripheral card is only allowed to perform DMA if its DMA_IN line is at logic ...
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How does DMACON/R registers on Commodore Amiga platform work?

I have a specific question about the DMACON/R registers found in Commodore Amiga range of computers. As you may know they are the DMA control registers that controls all the DMA channels used by the ...
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PC/AT two DMA controllers - what is the purpose of cascade channel and how did it work?

Why did the design need to reserve one channel for cascade, how did it work and what exactly was going on there?
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16 votes
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For how long can you safely stop the clock on an NMOS 6502?

As with most NMOS processors, the NMOS versions of the 6502 (and even earlier CMOS versions) do not have a static core. Thus, if you run the clock too slowly or stop the clock for too long while doing ...
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What is the exact bus protocol used by the C64/C128 REU?

The Commodore 64/128 RAM Expansion Units used a DMA controller to move data between the REU's RAM and system RAM (or I/O space). One would set the addreses, length and direction for the transfer (or ...
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9 votes
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what is DMA and how does it work?

I've heard the term 'DMA' being used a lot in reference to older consoles. My very basic understanding is that it's a way for the console to access memory directly. But directly as apposed to what? ...
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