Re: Serial Port extensions and multipliers

[Geoff Hargreaves <geoffwhargreaves@xxxxxxxxxxxxxx>]

  It is possible to transmit RS232 over long distances, but the longer
the distance, the lower the baud rate needs to be in order to reliably
transmit and receive the data. I know of an installation that transmits
RS232 down approx 100m of cable, but uses 300 baud, odd parity and 1
stop bit.

Most likely you will be needing to use higher baud rates, say 9600 or
higher. 15m isn't too long, so you will probably be OK. For long runs
(like the 100m I mentioned earlier) you would normally use balanced
leads and protocols such as RS422 or RS485. You can get converter boxes
to go at both ends of the cable to change RS232 to RS422 or RS485 and
back again.

If you daisy chain multiple serial ports together, all serial ports
receive all serial data. This could cause problems if more than one
device share common commands, as both will respond.  I have seen
instrumentation using the RS485 serial protocol that used addresses to
differentiate between them. So each command sent would be preceded by
the address of the device meant to receive it, thus only that device
would respond. I don't know if this is a feature of RS485 or was special
to the instruments being used.

It is possible to buy PCI serial cards or even USB to serial adaptors.

HTH

Geoff

On 08/10/2010 12:53, noughtomate wrote:
> Hi,
>
> I'm new to the world of RS232 comms and just figured out I can talk to
my Comfort alarm system using Serial port. I use the mControl home
automation software have been thinking of writing a few scripts to automate
arming and dis-arming.
>
> But aside from this, I am now considering control of my Amplifier,
Sky-HD box and others in my main lounge.
>
> But this is all new ground to me... So a few newbie questions :
>   - Does serial DB9 support connectivity over a long distance ? The
distance between my NodeZero and AV Stack is about 15 meters. I've
pre-wired 8 core alarm cable, CAT6 and Co-Ax...
>
>   - Can serial comms be port- multiplied ? i.e. Single Serial port
->  multiple receiver devices ?
>
> Whether the answer is yes or no, what's the workaround ?
>
> I would imagine most Motherboards support maximum of 1 or two serial
ports, so how do you guys get over this if you want to control more than 2
devices over a distance of say 15 meters ?
>
> Thanks
>
>
>
> ------------------------------------
>
>
> Yahoo! Groups Links
>
>
>


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