Hi
422 can be an impedance controlled line with terminations.
232 tends to be under driven on typical lines and unterminated.
This means that an 232 signal will look like a stair case to the
receiver input that on long runs may cause intermittent edges. At
lower baud rates, most 232 receivers can handle this much
distortion.
Also, since it is under driven, the signal can be corrupted
by even a small amount of outside noise. This is made even worse
because it is single ended and any common mode noise can corrupt
the signal.
In other words, just because you ran it in your house for 30
feet and never saw an error doesn't mean it can be done in all
cases.
422 is impedance controlled and can be used at baud rates
up to 5 or 10 MHz ( depending on manufacturer ). It can do this
until resistive losses bring the level too low to be detected.
Being differential, only common mode noise that pushed it
beyond the common mode will be an issue and if the noise is
short term, the receivers are designed to not switch the outputs
until they are brought back into the common mode.
I once designed a communications bus using RS-485 ( similar
to RS-422 ) lines to interconnect several machines in a noisy
environment. The previous design used RS-232 and was not robust
enough to work in that same environment. The lines were less
than 15 feet on the RS-232. The RS-485 setup ran for over 10 years
without logging a single bit of data loss ( there were several
component failures during that time that don't count ).
Dwight
>From: "Mike Feher" <n4fs_at_monmouth.com>
>
>
>OK, I may be wrong, ( will not be the first time) I do have the original
>Mil-STD or EIA specification on these interfaces, and admit that it is not
>my specialty, however, it is fact, to the best of my recollection, that 422
>will be reliable over a lot more distance than RS-232. I will dig out the
>document, when I get a chance and quote actual specified numbers. Regards -
>Mike
>
>
>
>Mike B. Feher, N4FS
>89 Arnold Blvd.
>Howell NJ, 07731
>(732) 901-9193
>
>
>----- Original Message -----
>From: "Sellam Ismail" <foo_at_siconic.com>
>To: <cctalk_at_classiccmp.org>
>Sent: Thursday, September 05, 2002 9:24 AM
>Subject: Re: EIA 232 vs. 422, Color Computers (was Re: Serial floppy
drives)
>
>
>> On Thu, 5 Sep 2002, Mike Feher wrote:
>>
>> > similar. 422 by the way is specified to go almost 1000 feet, while with
>232
>> > you are lucky to get over 10 feet. Regards - Mike
>>
>> That's not true. Serial cable can go for a good many feet before the
>> signal breaks down (someone should pipe in with actual data ;)
>>
>> Sellam Ismail Vintage Computer
>Festival
>>
--------------------------------------------------------------------------
>----
>> International Man of Intrigue and Danger
>http://www.vintage.org
>>
>> * Old computing resources for business and academia at
>www.VintageTech.com *
>>
>>
>
>
Received on Thu Sep 05 2002 - 17:34:00 BST