novaBBS - comp.sys.apple2 - Re: Pulling DMA low

Pulling DMA low

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Subject: Pulling DMA low
From: anthonyp...@gmail.com (Anthony Ortiz)
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by: Anthony Ortiz - Tue, 23 Aug 2022 17:53 UTC

Sorry for what might be a stupid question but I’ve been pulling the DMA line low by setting my gpio pin to output and clearing it, which sends a digital zero to the Dma line and that seems to work. However, searching online I see mention of simulating an open collector output by setting the gpio to input instead. I would like to do this the right way, so I’m wondering what the correct method is, and whether connecting it to ground will suffice.

Thanks in advance!

Re: Pulling DMA low

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by: Michael J. Mahon - Wed, 7 Sep 2022 00:41 UTC

Anthony Ortiz <anthonypaulo@gmail.com> wrote:
> Sorry for what might be a stupid question but I’ve been pulling the DMA
> line low by setting my gpio pin to output and clearing it, which sends a
> digital zero to the Dma line and that seems to work. However, searching
> online I see mention of simulating an open collector output by setting
> the gpio to input instead. I would like to do this the right way, so I’m
> wondering what the correct method is, and whether connecting it to ground will suffice.
>
> Thanks in advance!
>

If I understand correctly, to assert /DMA you switch the GPIO to “output”
and output “0”, and to de-assert it you switch the GPIO to “input”.

This is the functional equivalent of using an open collector gate, so
you’re fine!

--
-michael - NadaNet 3.1 and AppleCrate II: http://michaeljmahon.com

Re: Pulling DMA low

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Subject: Re: Pulling DMA low
From: anthonyp...@gmail.com (Anthony Ortiz)
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by: Anthony Ortiz - Wed, 7 Sep 2022 00:57 UTC

> If I understand correctly, to assert /DMA you switch the GPIO to “output”
> and output “0”, and to de-assert it you switch the GPIO to “input”.
>
> This is the functional equivalent of using an open collector gate, so
> you’re fine!
>
> --
> -michael - NadaNet 3.1 and AppleCrate II: http://michaeljmahon.com

Thanks Michael! You're the man!!

"All these black people are screwing up my democracy." - Ian Smith

computers / comp.sys.apple2 / Re: Pulling DMA low

Subject	Author
Pulling DMA low	Anthony Ortiz
Re: Pulling DMA low	Michael J. Mahon
Re: Pulling DMA low	Anthony Ortiz