[E3-hacking] Another hello

jchadd at amserve.net jchadd at amserve.net
Thu Jan 19 17:25:28 GMT 2006

The E3 and E2 have clamping diodes on the serial port's input 
and output pins. As such anything above 5V or below 0V is 
effectively shorted out. This is meant for ESD protection but 
I suppose the diodes will effectively clamp +/-12V RS232 to 0-
5V TTL. So long as the PC doesn't supply too much current and 
warm the diodes up too much!

John Chadd

Cliff Lawson wrote:
> I'd have thought the protection was vital. It's not so much 
whether the PC
> can detect the "weedy" 0V..5V swing coming out of an E2/E3 
but whether the
> UART input buffers on the OMAP/Sharp can stand getting -12V 
shoved up them
> coming from the PC (I'm assuming that PCs still transmits 
true RS232 even if
> they're a bit more lenient about what they can detect?)
> (Or maybe my h/w designing colleague did splash for 
sufficient inbound
> protection on the board - I can't remember off hand)

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