Re: Serial Port Question

From: Richard Atkinson (
Date: 2000-08-18 19:25:43

On Fri, 18 Aug 2000, Mike Naberezny wrote:

> I decided I might try and make a simple "switch" for one of my serial port
> devices.  To do this, I used a 4066 quad bi-lateral switch IC.  Four of
> the serial port lines are switched: SRQIN, ATN, CLK, and DATA.  GNDs were
> just tied together and RESET was left out for now.  I put the "switch" in
> between my C128 and a drive with all four of the 4066 switches on.  The
> C128 doesn't see the drive.  I used an ohmmeter to test the two cables
> plugged into my "switch", all four pins are connected correctly with about
> 300 ohms resistance between.  Any ideas why it didn't work, or a possible
> solution?  

How are you powering the 4066? An analogue switch needs the various supply
terminals to be held at the correct potentials, otherwise nasty things can
happen with latchup.

Other than that, I can only suggest that the extra resistance is causing
problems with burst mode (due to larger R in RC time constants) so perhaps
you might consider trying it with a C64 (or in 64 mode).

Connect RESET straight through between all ports, by the way - there's no
harm in resetting all devices at once.


Richard Atkinson
Software Engineer
Tenison Technology EDA Ltd

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