Re: max IEC bus length and loading?

From: Nate Lawson <>
Date: Wed, 03 Nov 2010 13:02:00 -0700
Message-ID: <>
> On Sun, 31 Oct 2010 11:57:27 -0700
> Nate Lawson <> wrote:
>> We have been doing some robustness testing of the ZoomFloppy board. It
>> uses a 7406 for driving the lines in order to be able to sink a decent
>> amount of current to support multiple IEC devices on the bus.
>> 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.

No one has supplied concrete info about bus characteristics, so we'll
have to just go with what we measure for 4 drives and various lengths of


       Message was sent through the cbm-hackers mailing list
Received on 2010-11-03 21:00:09

Archive generated by hypermail 2.2.0.