🚀 go-pugleaf

In article <C1Ewyx.2ny@dcs.ed.ac.uk> gst@dcs.ed.ac.uk (George Taylor) writes:
>The engineer at Norwhich Computer Services ...
>suggests extreme care be taken with the port and that screened (hence earthing
>from one machine's chasis to another) leads and plugs should always be used.

Screened leads, yes, but the screen should be connected at one end only and
not used to provide an earth connection to either machine. This is because
(a) it can cause an earth loop if both machines are earthed and (b) the
chassis of the two machines may not be at the same potential particularly if
they are remote. This is why there is a separate signal ground connection
which is effectively a common return path for the other signals.

Richard

In article <C1Ewyx.2ny@dcs.ed.ac.uk> gst@dcs.ed.ac.uk writes:

>Further to my previous posting concerning my record of faulty serial ports, I
> now
>have my machine back and working.
>
>The engineer at Norwhich Computer Services reports
>that the serial driver chip had suffered static damage (the driver chip is a
> CMOS
>device which uses a charge pump to create the +/- RS232 voltages).
>He suggests extreme care be taken with the port and that screened (hence
> earthing
>from one machine's chasis to another) leads and plugs should always be used.
>I would have thought that given the typical nature of serial port use (noisy
>environments etc) that CMOS drivers are a bad idea, I intend to make up my own
>buffer to protect my port. I have never heard of this problem occuring on
>other euqipment using serial ports.
Generally on serial hardware you're not supposed to connect PG (pin 1 on
25-way) to the PG on the other end (or so I was told). As the 9-pin has
no PG, I don't know what you really should do.

A3000 serial ports never seem to blow when they've been working before... 
however, I know of *many* people who have got the chips and had them D.O.A.

The old A5000's use the same method (ie charge pumps), as does our serial
card (socketed AD238's). I note with interest that the A3010/4000 use the
(very) tried and tested 1488/1489 combination with unregulated +/-12v
supply (nice you you've got it). Bombproof, practically, the way it used
to be done in 'the good old days'.

Hugo
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                                     "Did I say that? My lips didn't move..."
Hugo Fiennes - The Serial Port                      altman@cryton.demon.co.uk
                                                or altman@cix.compulink.co.uk
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