AVR-Chat

Russell Shaw wrote:
> I run rs232 from my workroom to the garage (30m).
I'm sorry to hear that, I'd do the same if I had nothing else. I would 
use RS-422 (not 485) "IF" I needed higher baud rates. The cables are 
usually 4-core + shield so I would not be at any loss. Termination is 
really only needed for high-speed operation as the reflections have 
negligible effect at RS-232 speeds anyway. I've run kilometres of 
cabling in skyscrapers with simple multi-node 19.2K RS-485 networking 
over untwisted fire-proof cabling without the "need" for termination 
even though the cables were not in any ordered configuration. Impossible 
with RS-232.
>
> At my previous job, rs232 was run from the lab to various measuring equipment
> outside (10-20m).
>
> I know of several radio hams that run rs232 from their radio room to things
> outside and up radio towers (10-30m).
>
> RS232 was designed for unterminated lines which keeps things simple,
> especially for multi-drop star networks. RS485 requires a single backbone
> with terminator.
RS-232 is not multidrop and at the low speeds it operates at would not 
need termination.
>
> RS232 can be fed thru radio coax and separated out with a filter, unlike
> rs485 which requires a balanced line.
Cool, I like that, but is it really real RS-232 anymore? (I think not)

>
> http://www.rs485.com/rs485spec.html
>
> RS485 requires three wires but rs232 only needs two.

Place a 1.5V battery across the balanced line to generate a signal, then 
reverse it to invert the signal. Did it require a separate ground? No! 
It is out of ignorance that a ground is connected, it is simply provided 
either for additional shielding or for kludging a particularly bad 
ground loop problem. By powering the remote equipment from the line it 
obviates the need for isolation.

Anyway, I like the fact that you are not strictly abiding by the 
standard and doing what engineers do best .... tinkering ;)


*Peter*