Diacom plus on Pentium laptops

[xxalexx at ix.netcom.com]

> Date:          Wed, 29 Jul 1998 09:04:09 -0400
> From:          Ken Kelly <kenkelly at lucent.com>
> Organization:  Lucent Technologies
> To:            diy_efi at efi332.eng.ohio-state.edu
> Subject:       Re: Diacom plus on Pentium laptops
> Reply-to:      diy_efi at efi332.eng.ohio-state.edu

> TBK,
>  
>  I believe you are correct on the 4 interfaces that Rinda is
>  compatible with, but the Diacom cable would have to have a
>  -10 to -12 volt supply to be able to create an RS-232
>  signal. The Maxim chips now make that easy, but I don't
>  think they were available when Rinda started the Diacom. Do
>  you really think the Rinda cable attempts to actively shift
>  levels? I thought the circuitry just shifted the pinouts
>  around for the various standards.
>                  Ken
>  
It is a well known undocumented hacker fact that rs232 chips 
will recieve the rs232 negative high level as anything under about
positive 1 V  and rs232 low over about 2.5 V, thus you do
not need a negative supply.  You would need a inverter to recognize
the start and stop bits.  Most people do not recommend useing over
10 feet, I have transmitted over 100ft for several days at 9600 baud 
in a automotive test envirnoment.
Last year I was looking at some Dodge OBD2 data at 8192 baud using
this method, also developed scan tool for OBD2 ISO9141 10400 baud
using rs232 inverted logic. 
It is a good idea to buffer the parallel port inputs.
You might search Jan Axelson for parallel port interfacing and 
current specs.
alex