Daisychaining when one device is off

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Eric Christopherson

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Jul 9, 2015, 1:33:57 AM7/9/15
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I notice that when I daisychain my 1581 in the first position and the
uIEC in the second, the uIEC still works with the 1581 off -- but only
on my actual Commodore. When I have them hooked up to the PC via XA1541,
I need to have the 1581 on.

Why is this?

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Eric Christopherson

RETRO Innovations

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Jul 9, 2015, 1:48:53 AM7/9/15
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> Unpowered devices drag the bus lines down. But, each powered device
> (and the 64/128) have pullup resistors. If the XA1541 does not, it
> might not keep the bus high enough to counteract the pulldown of the
> unpowered 1581.

Jim


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RETRO Innovations, Contemporary Gear for Classic Systems
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Eric Christopherson

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Jul 9, 2015, 2:08:55 AM7/9/15
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On Thu, Jul 09, 2015, RETRO Innovations wrote:
> On 7/9/2015 12:33 AM, Eric Christopherson wrote:
> >I notice that when I daisychain my 1581 in the first position and the
> >uIEC in the second, the uIEC still works with the 1581 off -- but only
> >on my actual Commodore. When I have them hooked up to the PC via XA1541,
> >I need to have the 1581 on.
> >
> >Why is this?
> >
> >Unpowered devices drag the bus lines down. But, each powered device (and
> >the 64/128) have pullup resistors. If the XA1541 does not, it might not
> >keep the bus high enough to counteract the pulldown of the unpowered 1581.
>
> Jim

Great to know. I've heard of those resistors before but never realized
what they were for.

--
Eric Christopherson
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