[Klug-general] TTL to RS-232 advice

[Mike Evans]

James,

My understanding is that they shift both ways.  Regulating the level 
back down to TTL is pretty simple - it's the boosting it up that 
requires a non-trivial pump.  The problem is in raising the usual TTL 
levels (from about 3V to 5V) up to the spec for RS232 (about 19V from 
memory).  Most devices contain the same chip (MAX232 - which is purpose 
built for it.)  Note that some RS232 devices/interfaces don't insist on 
the 19V levels and will work fine with a low voltage input so you can 
always try - particularly if the lead is short.)

USB has different driver circuitry again.

Mike

On 03/01/15 16:35, jwmartnet . wrote:
>
> Hi,
>
> I want to connect a serial console to my device but need a bit of 
> advice before purchasing components.
>
> According to the article linked below, I need a ' 3.3V TTL to RS-232 
> level shifter'
>
> http://www.cyrius.com/debian/kirkwood/qnap/ts-219/serial/
>
> Do these converters work bidirectional? Or does it specifically need 
> to be 3.3V TTL to RS-232 and not RS232 to 3.3v TTL?
>
> Anything to avoid?
>
> Probably wishful thinking, but.. I guess TTL to USB wouldn't work 
> without intervening electronics?
>
> Cheers
> James
>
>
>
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