What is RS485?
Dave Kolb
many wires, types of connectors etc.
Thanks,
Dave Kolb
Nigel Orr
<dave...@email.msn.com> wrote:
>I understand RS232 just fine but have never used RS485. What uses it and how
>many wires, types of connectors etc.
RS485 doesn't decree types of connectors, or data protocols, just how
the signal gets down the wire.
RS422 is probably easier to describe first- it's just like RS232, but
the signals are differential, so instead of 1 wire for transmit and 1
wire for receive, you have a pair for transmit and a pair for receive.
This allows it to be more immune to noise over longer distances.
RS485 is similar, except instead of just one unit at each end of the
cable, you can have many units, each of which may be able to receive
or transmit. Only one unit should be allowed to transmit at a time,
and the others have to be able to set themselves to 'high impedance'
when not transmitting to avoid interference with the legitimate
transmission.
As an example, I've recently built a parallel to RS485 to parallel
port converter, to allow a device which normally connects directly to
a PC parallel port to be placed at the end of 120m of cable instead.
There is one 'bus', a single twisted pair cable which handles
communications in both directions.
Hope that helps,
Nigel
Dave Houston
>I understand RS232 just fine but have never used RS485. What uses it and how
>many wires, types of connectors etc.
>
>Thanks,
>
>Dave Kolb
>
For a brief explanation, see...
http://www.lantronix.com/htmfiles/ts/techtip/faq/faq0064.htm
For a more complete understanding, buy Jan Axelson's book "Serial Port
Complete".
RS-485 can be 4-wire or 2-wire. According to the book cited above, 2-wire,
multi-drop is the version that is most widely used.
The ADICON modules that Applied Digital has for their CPU-XA are 2-wire,
multi-drop. B&B Electronics makes numerous I/O modules and most of them can
be used in either 2-wire or 4-wire networks. B&B also has some application
notes that are excellent.
Dave Houston
http://Commander-X.com
Robert.
is a great improvement for home automation controllers that offer a RS-485
port. You can connect multiple devices (of different types) to one RS-485
port. For example, on the JDS Stargate, you can connect up to 16 RCS
thermostats on one RS-485 port. Or, you could connect up to 16 of the LCD
keypad that JDS will be releasing this summer. Or you could use a
combination of both of these devices on the one port. The LCD keypads only
need one pair of wires to communicate with Stargate.
Robert
RCI Automation
rciaut...@csi.com
http://ourworld.compuserve.com/homepages/rciautomation
Dave Kolb wrote in message ...
Tim Shephard
You can see a description of it on my home page below.
-Tim
tim.sh...@bigfoot.com
tims....@bigfoot.com
http://www.bigfoot.com/~tim.shephard/tim/ha
eFax (508) 590-0302
Robert. wrote in message <3sg13.9814$U83.2...@news.san.rr.com>...
Robert.
I checked out your Stargate TV output and it looks great. On the sample
screen shot of the temperatures, are you feeding the PIC-TV output into the
modulator on a separate channel (separate from your front door camera
channel)? I was wondering because you mentioned the video camera at your
front door and on the screen shot I see a blue background. Or, does the
PIC-TV overlay the modulated camera signal when it detects input? How did
you specify that the display only show for 15 seconds?
Thanks,
Robert
RCI Automation
rciaut...@csi.com
http://ourworld.compuserve.com/homepages/rciautomation
Tim Shephard wrote in message <7i4oa3$nao$1...@ash.prod.itd.earthlink.net>...
Tim Shephard
colors, or you can overlay the text on the current video that is on the
video in jack on the module.
In this case, since I already had a video modulator for my front door
camera, I used that so I could have Stargate text to all the TV's in the
house. Using simple ascii commands, StarGate commands the PIC-TV to use a
blue background with white letters (easier for me to read).
If I wanted, I could have the PIC-TV display the text over the top of the
front door video. In fact, I could have it setup that if I was viewing the
temperature screen, and front door motion was detected, StarGate could send
the \k command to the PIC-TV, that would leave the text unchanged, and show
the front door video on the background.
As far as the delay goes. If you look at the sample code:
DELAY 0:00:15
ASCII-Out:'! TERM0 S=\k' [RS-485]
ASCII-Out:'! TERM0 S=\f' [RS-485]
After the delay, the \k command switches back to overlay mode, so I can see
the front door camera output (there is also an OFF command \c but I have not
tried that) and the \f command clears the screen of the text.
-Tim
tim.sh...@bigfoot.com
tims....@bigfoot.com
http://www.bigfoot.com/~tim.shephard/tim/ha
eFax (508) 590-0302
Robert. wrote in message ...
Dave Kolb
Dave Kolb