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Old 06-02-2007, 08:59 AM
cdvs cdvs is offline
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Join Date: Mar 2007
Location: Oakham, MA
Posts: 197
Quote:
Originally Posted by b3lha
What you said about RS232 is correct, but the ECU does not use RS232. It has a UART, but the signaling is done at TTL levels.
For those that don't know UART is Universal Asynchronous Receiver Transmitter. It refers to the hardware device used to implement RS232 which is the engineering standard for asynchronous comminications.

TTL levels are +5 to -5 and fall within the RS232 spec. AFAIK, the only reason to use higher voltages is to overcome line losses that occur over long distances. This is not an issue here.

Quote:
Originally Posted by b3lha
The guys on the Legacy forum are using a simpler interface made from a couple of resistors, a diode and a transistor.
What this simple circuit adds are always on request to send and clear to send signals. These signal lines were incorporated to overcome a devices processing limitations. This became a non-issue around 1970 and are rarely, if ever, used today. Anyway, what this stuff does is defeat their purpose. Something akin to fingernail polish. It might look good and doesn't hurt anything, but serves no useful purpose.

Quote:
Originally Posted by b3lha
Seriously, if you think you have a better way, please try it and report back the results so we can all benefit from your experience.
I'm not out to prove anything. I was attempting to make a contribution. I would have preferred to test this, but I don't have the time. I'm over-indulging my interest just making these posts. Someone else will have to carry the ball from here, or not.

Charl
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