Re: max IEC bus length and loading?

From: Nate Lawson <>
Date: Sun, 07 Nov 2010 13:12:27 -0800
Message-ID: <>
On 11/7/2010 7:24 AM, wrote:
> Quoting Nate Lawson:
>>>> What is the defined worst-case IEC bus configuration that we should
>>>> support? I'd like a reasonable limit we can support while not adding too
>>>> much delay for users of one or two drives.
>> Just to summarize the discussion:
>> Most people think 4 drives is enough. Some want 6 or 8 devices,
>> including printers.
>> The 7406 total recommended sink current is 40 mA, max is 60 mA. That is
>> 8 or 12 drive-equivalents at 1k ohm, respectively. For 2 lines
>> simultaneously-held (say, CLK & DATA), that allows 4 drives. The max
>> value allows 4 drives and 3 lines (CLK/DATA/ATN, for example). So I
>> believe we can comfortably access 4 drives, given a short enough total
>> cable length and pessimistic enough delays.
> I tried to find characteristics, which is surprisingly difficult.
> I came over a book called : "Commodore 1541 Troubleshooting and Repair guide" 
> by Michael G. Peltier.
> On Page 154, there is a big WARNING not to connect more than 5 drives.
> Please check: 
> I hope that somehow answers your question (albeit in a vague and roundabout 
> way, I'm afraid)

Thanks for the reference. While that isn't an authoritative standard,
it's nice to have some kind of reference.

I think we will target 4 drives with some kind of max bus length and
document that in the README. We will try to allow it to work with more
devices, but no guarantees. Really, if you want more drives, just get
another ZoomFloppy.  :-)


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Received on 2010-11-07 22:00:10

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