On 2/26/23 12:16, Mike Stein wrote:
Ah, got it; I was asking about switching it from the keyboard as the XR4
does, not a physical switch.
But if you're just talking about a small number of selections then tiny
diodes would probably work just as well and not require any power.
I guess you're right, since it's only OR gates and positive logic, those
could just as well be common cathode pairs of diodes, and they are
available in a single 6-pin package, and it needs one fewer resistors
because instead of pulling down the 3 inputs, you pull down the two
outputs, though that doesn't really save me anything because I'm using a
single 4-resistor part.
It doesn't save much in absolute terms, like cost or real estate, but it
still does remove a bit of power and trace routing and trades a fancier
part for a more common and basic part.
I'll try it.
m
On Sun, Feb 26, 2023 at 9:52 AM Brian K. White <[email protected]
<mailto:[email protected]>> wrote:
On 2/26/23 08:23, Stephen Adolph wrote:
> Brian, If I understand your comment, I don't think you need an IC
to do
> rom selection. I think the DAR uses a rotary encoder.
I understand that the dar uses a rotary encoder.
The slide switch needs the extra glue.
I was responding to Mike's question "how does the bank select work?"
answer: gratuitous extra parts because I just wanted a slide switch.
> When I first saw the DAR, I wondered about that. I'm pretty sure
I found
> the part at Digikey. Very good!
> Steve
>
> On Sun, Feb 26, 2023 at 3:51 AM Brian White <[email protected]
<mailto:[email protected]>
> <mailto:[email protected] <mailto:[email protected]>>> wrote:
>
> Gratuitous use of another chip just for 2 OR gates to implement a
> 4:2 encoder. It's all less efficient and less practical than the
> dial-a-rom, in that the dar holds 16 roms and doesn't need
another
> ic, and the dar programming connection is even simpler and
more robust.
>
> But it just amused me to have a direct selector without manually
> binary encoding dip switches because why not? And I didn't
want it
> to require a tool to use either like a screwdriver. And of
course I
> always want an open source option, and I'm not up to the task of
> coming up with an open source rex-alike but using a Lattice
part and
> the open source toolchain.
>
> It's unfortunate timing but I had already started this at least 3
> years ago but just never finished it. A non-working version
has been
> sitting in that github since 2019. A few weeks ago I finally
dusted
> it off and corrected my bonehead pinout error, dialled-in the
> programming connection so it works well (the holes are slightly
> closer together than the pins, and the pattern and amount of
offset
> took some trial & error) and replaced dip switches with the slide
> switch & or gates. I had no idea the dar was in the works.
Not that
> it would have stopped me, but I just mean to say this isn't a
reaction.
>
> It's no competition anyway because only a very few people
ever build
> these diy-only things. I want them to exist so the option is
there,
> but almost no one actually employs it. So this is not touching
> anyone's sales. Besides, *16* roms. And of course really it's
even
> sillier when rex exists which doesn't even need a programmer or
> adapter to load it's, what, 30? slots? But for other
platforms 4 is
> plenty. There's only 2 roms total for the 600 for example. Still
> leaves 2 free slots for hacking.
>
> I just added the browser-friendly render of the schematic to the
> readme so you can see the bank-select.
>
> --
> bkw
>
> On Sat, Feb 25, 2023, 8:18 PM Mike Stein <[email protected]
<mailto:[email protected]>
> <mailto:[email protected] <mailto:[email protected]>>> wrote:
>
> How do you select among the 4 images?
>
> On Sat, Feb 25, 2023 at 6:50 PM Brian K. White
> <[email protected] <mailto:[email protected]>
<mailto:[email protected] <mailto:[email protected]>>> wrote:
>
> On 2/25/23 10:31, [email protected]
<mailto:[email protected]>
> <mailto:[email protected]
<mailto:[email protected]>> wrote:
> > Morning all,
> >
> > I just made this video live this AM. The DARs for the
> Model T computers
> > have sold out already but my friend is making more.
> >
> > In this video we take a look at the ‘Dial-A-ROM’ a
spiffy
> new multi-ROM
> > for vintage portable computers. It was designed by the
> same guy who did
> > the Backpack drive. First, we’ll learn how to use the
> Dial-A-ROM with
> > the ROM images that come preinstalled on it. Then
we’ll
> see how to add
> > our own ROM images if we so desire.
> >
> > *https://youtu.be/CejyLsI0HIw
<https://youtu.be/CejyLsI0HIw>
> <https://youtu.be/CejyLsI0HIw
<https://youtu.be/CejyLsI0HIw>> <https://youtu.be/CejyLsI0HIw
<https://youtu.be/CejyLsI0HIw>
> <https://youtu.be/CejyLsI0HIw
<https://youtu.be/CejyLsI0HIw>>>
> >
> > Jeff Birt (Hey Birt!)*
> >
>
> And for the diy-er, I finally vetted these last week:
> https://github.com/bkw777/Teeprom/blob/master/4ROM.md
<https://github.com/bkw777/Teeprom/blob/master/4ROM.md>
>
<https://github.com/bkw777/Teeprom/blob/master/4ROM.md
<https://github.com/bkw777/Teeprom/blob/master/4ROM.md>>
>
> --
> bkw
>
--
bkw
--
bkw
