Which RS232 IC?


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  1. #1
    Prolific Poster pic-ignorant's Avatar
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    Default Which RS232 IC?

    Hi All

    I'm looking to do serial comms between 2 PICs at up to 60 feet apart. Looking through RS, there are literally 100's of transceivers to choose from. Could anybody recommend a tried and tested part? Preferrably not too expensive.

    Thanks for any advice

    John

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  3. #2
    joantabb
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    Default Re: Which RS232 IC?

    I believe 60 feet is beyond the specified maximum distance for an RS232 link, it will probably work, but if it didn't you'll get little help from the suppliers...

    you could try RS485 or RS422, both of which are rated for much greater distances.

    regards John

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    Junior Member g6osv's Avatar
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    Default Re: Which RS232 IC?

    Is it a one off or a production? In have somewhere a couple of these LDM30 that you can have for just postage to try out.
    http://www.dataforth.com/document.view.aspx?doc_id=221
    Ian

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  7. #4
    hadv215
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    Default Re: Which RS232 IC?

    Depends on the Baud Rate, see this link http://www.lammertbies.nl/comm/info/RS-232_specs.html

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    ADLIN SYSTEMS
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    Default Re: Which RS232 IC?

    I used a maxim rs232 chip and got 100 meters with 4 core alarm wire no handshaking and all worked great at 19200 baud.


    Anton

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  11. #6
    rverm
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    Default Re: Which RS232 IC?

    my last job we did repairs on rs485 networks. they were several hundred feet long with termination resistors at each end of the network. about 120ohms to keep the noise down.

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    Prolific Poster pic-ignorant's Avatar
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    Default Re: Which RS232 IC?

    Thank You all for the replies.
    Hi Ian, ty for the offer but I need lots of them, and space is very tight.
    After a proper check, the actual cable length is unlikely to be longer than 25 feet. I believe this is ok for rs232?

    I must confess, I know nothing about RS485 or RS422. Will the Proton serial commands work ok with a RS485/422 transceiver?

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    Kapitan
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    Default Re: Which RS232 IC?

    Quote Originally Posted by pic-ignorant View Post
    Hi All

    I'm looking to do serial comms between 2 PICs at up to 60 feet apart. Looking through RS, there are literally 100's of transceivers to choose from. Could anybody recommend a tried and tested part? Preferrably not too expensive.

    Thanks for any advice
    John
    Hiya John
    If you are using software serial, no worries re transceiver depending on distance, you would have to try it.. but the best option, and the one I use almost all the time, is Les's 2 transistor unit to do the inversion, its listed in the proton help file. I would imagine that using SMT parts, the cost and component count would be comparable or in fact less than other methods.
    Also, cos you are talking just to another pic (r) then, you dont need the original full rs232... even talking to nmea devices which I understand are in fact 423.. or certainly to a usb serial converter or pc / laptop, no worries.
    It is a super. low component count way.. my proton development board finally died in the area of the max232. so just snipped a few tracks, blew it away and built the two transistor solution on the back of the board.. all great again
    It is really worth considering !.
    Joe.

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  17. #9
    joantabb
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    Default Re: Which RS232 IC?

    RS232, in it's simplest form is a NRZ (Non Return to Zero) signalling protocol where the transmit and receive wires carry signals which vary in polarity relative to a common ground signal. These are OK for short distances but suffer from poor noise rejection. fficeffice" />>>
    RS485 and RS422 are the line protocols and can deliver the same information as is used normally to drive an RS232 solution, so the code from proton would be largely the same. Where these protocols differ, is in the signals sent over the wires to deliver service. RS485 and RS422 both use two wires for transmit and two wires for receive (Full Duplex) and the signalling on the two transmit wires consists of opposed balanced NRZ signals, these balanced signals are better able to overcome electrical noise injected from external sources, making the protocol more resistant to interference over greater distances.>>
    >>
    RS485 can be used for a multi drop solution where data is sent to a number of different devices on a common circuit, we use them for call centre wallboards, where all wallboards connect to the same cabling, but the messages are preceded by an address, and the wallboards are aware of their own particular address. So only respond to either their own address messages, or broadcast messages where all of the address bits are "0's">>
    This allows us to deploy wallboards on several floors of the building without problems; I have also just used pairs of rs232 - rs485 line extenders to extend serial data from a telephone system to a serial "point of sale" printer, over a hundred metres away. Using voice quality twisted pair cable. >>
    >>
    RS485 can be used it two different modes, these are Half Duplex, and Full Duplex. >>
    >>
    Half duplex requires the end devices to rest in the receive state, listening for communication, and then switch to the transmit state to send data... (This permits service on a smaller number of conductors in the interconnecting wire) so signals can only go one way at a time... >>
    Full Duplex requires more wires, but simplifies the solution by not requiring switching between transmit and receive... >>
    >>
    RS422 is usually a point to point that uses a similar line code to RS485

    Hope this helps,

    regards JOhn>>
    >>

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    Fanatical Contributor fanie's Avatar
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    Default Re: Which RS232 IC?

    Suggested use for RS232

    RS232 Data per cable length
    Maximum Data Rate (bps)
    Maximum Length)
    2,400 (2.4K)
    120m (400ft)
    4,800 (4.8K)
    60m (200ft)
    9,600 (9.6K)
    30m (100ft)
    19,200 (19.2K)
    15m (50ft)
    38,400 (38.4)
    7.5m (25ft)
    57,600 (57.6K)
    5.0m (16ft)
    115,200 (115.2K)
    2.5m (8ft)
    Fanie

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