AVR-Chat

Thomas Keller wrote:
> Russell Shaw wrote:
> 
>>Peter Jakacki wrote:
>>
>>>Russell Shaw wrote:
>>>
>>>>It is no different now than then. Back then, RS232 was run around and
>>>>between buildings for terminals and mainframes. If you still want to
>>>>run those distances, you'll want +/-15V
>>>
>>>No, it is different and that is just the point. Nobody runs RS-232
>>>between buildings, do you? If we don't go as far as using fibre then we
>>>would use a balanced line drive like RS-422, but never ever RS-232. 
>>
>>Yes,
>>
>>>I still want to run those distance, but no, I am not stuck in the 60's
>>>because I use RS-422/485 or some other means.
>>
>>I run rs232 from my workroom to the garage (30m).
> 
>   Perhaps so.  That doesn't make your practice reasonable.

Why?

>>At my previous job, rs232 was run from the lab to various measuring 
>>equipment outside (10-20m).
> 
>   Poor engineering management?

Why?

>>I know of several radio hams that run rs232 from their radio room to 
>>things outside and up radio towers (10-30m).
> 
>   With all due respect to radio amateurs, who, as a group, have 
> contributed greatly to the advancment of communications technology, they 
> *ARE*, by self-definition, amateurs, after all.

Yes but they do a better job of grounding and interference suppression
than most so called "engineers" that are barely more than tinkerers.

>>RS232 was designed for unterminated lines which keeps things simple,
>>especially for multi-drop star networks. RS485 requires a single backbone
>>with terminator.
>>RS232 can be fed thru radio coax and separated out with a filter, unlike
>>rs485 which requires a balanced line.
>>http://www.rs485.com/rs485spec.html
>>RS485 requires three wires but rs232 only needs two.
> 
>   Not the last time I looked.  Unless you are making a unidirectional 
> connection, you need at LEAST 3 wires for a proper RS232-C link.  
> Ground, TX and RX.

That's what i said before, unless the line is half-duplex.