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computers / comp.sys.apple2 / Re: Apple II TTL to 3.3 logic

SubjectAuthor
* Apple II TTL to 3.3 logicAnthony Ortiz
`* Re: Apple II TTL to 3.3 logicMichael J. Mahon
 `* Re: Apple II TTL to 3.3 logicAnthony Ortiz
  `- Re: Apple II TTL to 3.3 logicDavid Schmidt

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Apple II TTL to 3.3 logic

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Subject: Apple II TTL to 3.3 logic
From: anthonyp...@gmail.com (Anthony Ortiz)
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 by: Anthony Ortiz - Tue, 19 Jul 2022 05:29 UTC

I'm redesigning some circuitry I have on my peripheral board to a modern 3.3v CPLD and read some articles on the interwebs stating that TTL logic is about 3.4 volts so I might get away with interfacing a 3.3 chip straight from the Apple IIe bus and do away with the 245 transceivers I'm using. My gut feeling is to have the 245's there just in case and err on the safe side, but I'm curious as to what you guys think about going raw from the Apple II bus to a 3.3v GPIO that's not that tolerant.

Re: Apple II TTL to 3.3 logic

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Subject: Re: Apple II TTL to 3.3 logic
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From: mjma...@aol.com (Michael J. Mahon)
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 by: Michael J. Mahon - Wed, 20 Jul 2022 02:05 UTC

Anthony Ortiz <anthonypaulo@gmail.com> wrote:
> I'm redesigning some circuitry I have on my peripheral board to a modern
> 3.3v CPLD and read some articles on the interwebs stating that TTL logic
> is about 3.4 volts so I might get away with interfacing a 3.3 chip
> straight from the Apple IIe bus and do away with the 245 transceivers I'm
> using. My gut feeling is to have the 245's there just in case and err on
> the safe side, but I'm curious as to what you guys think about going raw
> from the Apple II bus to a 3.3v GPIO that's not that tolerant.
>

Nope—you’ll need level-changing circuitry and keep the 245’s. The Apple II
bus is *definitly* a TTL bus.

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

Re: Apple II TTL to 3.3 logic

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Subject: Re: Apple II TTL to 3.3 logic
From: anthonyp...@gmail.com (Anthony Ortiz)
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 by: Anthony Ortiz - Wed, 20 Jul 2022 02:10 UTC

On Tuesday, July 19, 2022 at 10:05:57 PM UTC-4, Michael J. Mahon wrote:
> > I'm redesigning some circuitry I have on my peripheral board to a modern
> > 3.3v CPLD and read some articles on the interwebs stating that TTL logic
> > is about 3.4 volts so I might get away with interfacing a 3.3 chip
> > straight from the Apple IIe bus and do away with the 245 transceivers I'm
> > using. My gut feeling is to have the 245's there just in case and err on
> > the safe side, but I'm curious as to what you guys think about going raw
> > from the Apple II bus to a 3.3v GPIO that's not that tolerant.
> >
> Nope—you’ll need level-changing circuitry and keep the 245’s. The Apple II
> bus is *definitly* a TTL bus.
>
> --
> -michael - NadaNet 3.1 and AppleCrate II: http://michaeljmahon.com

Thanks Michael, you're always a great help and an invaluable source of all things Apple II. :)

Re: Apple II TTL to 3.3 logic

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From: schmi...@my-deja.com (David Schmidt)
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Subject: Re: Apple II TTL to 3.3 logic
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 by: David Schmidt - Wed, 20 Jul 2022 06:04 UTC

On 7/19/22 10:10 PM, Anthony Ortiz wrote:
> On Tuesday, July 19, 2022 at 10:05:57 PM UTC-4, Michael J. Mahon wrote:
>>> I'm redesigning some circuitry I have on my peripheral board to a modern
>>> 3.3v CPLD and read some articles on the interwebs stating that TTL logic
>>> is about 3.4 volts so I might get away with interfacing a 3.3 chip
>>> straight from the Apple IIe bus and do away with the 245 transceivers I'm
>>> using. My gut feeling is to have the 245's there just in case and err on
>>> the safe side, but I'm curious as to what you guys think about going raw
>>> from the Apple II bus to a 3.3v GPIO that's not that tolerant.
>>>
>> Nope—you’ll need level-changing circuitry and keep the 245’s. The Apple II
>> bus is *definitly* a TTL bus.
>>
>> --
>> -michael - NadaNet 3.1 and AppleCrate II: http://michaeljmahon.com
>
> Thanks Michael, you're always a great help and an invaluable source of all things Apple II. :)

I have to agree. What an absolute treasure you are, Michael. Thank you.

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