RE: Re: RS232/482 Qs

["Kevin Hawkins" <lists@xxxxxxx>]

    Tim, what actually is the distance you are talking about going to work out at ?

 

    Most alarm systems use 485 for their comms what system is it ? On some systems e.g. Comfort you can separate the RS232 from the panel and the connection works over very long distances and has error checking built in.

 

    RS232 is quite flexible and at low speeds the distances it can run on are much higher. I would suggest you measure the distances involved and make up a cable and try it - that way you will know if it is going to be a problem in advance - even better make it up much longer and then you have some level for error.

 

    Perhaps most importantly is there an error checking protocol running on the RS232 ?? and/or is it a 'critical' link in terms of data integrity ?

 

    At a previous company following the acquisition of an adjacent building we had VT100 terminal attached to a Vax 'mainframe/mini' running over 250m at 9600 baud - we did not notice any problems but it is way outside the spec. My Slink-E connection here is a good 75m too.

 

    If you embed cables and you use twisted pair of some form then you could later switch from RS232 to 485 if problems occurred. You need to check how many wires are required for both the RS232 and the 485 connection. The RS232 will be somewhere between 3 minimum, 6 or 7 typically and lots in a very complex (rare) situation. The RS485 will require a couple more due to the twisted pairs. It also may be a separate transmit and receive pair or in some cases a more complex shared pair.

 

    Perhaps someone else can put in their view on shielding - in one sense it cuts down on noise on the link, adding to the distance possible but in another it adds to the capacitance which adversely effects the distance particularly at high data rates, although 9600 is not very high. Is the locality of the cable electrically noisy ?

 

    Kevin

 

-----Original Message-----
From: Timothy Morris [mailto:timothy.morris@xxxxxxx]
Sent: 11 May 2002 14:25
To: ukha_d@xxxxxxxSubject: RE: [ukha_d] Re: RS232/482 Qs

No, It's just for the link between the PC and the HA controller/Alarm
system. I need to spec the stuff to go in the walls, I presume a
standard 4/8 core shielded cable will be more than adequate?

Tim.

-----Original Message-----
From: PatrickLidstone [mailto:patrickl@xxxxxxx]
Sent: 11 May 2002 13:49
To: ukha_d@xxxxxxxSubject: [ukha_d] Re: RS232/482 Qs

PS. If this run is going outside, for CCTV camera control or
whatever, I'd use external line drivers for lightning protection...

Patrick



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