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SN75176B: What is the best transceiver and cable model for my application?

Edemilso Ilha
Prodigy 10 points
Part Number: SN75176B
Other Parts Discussed in Thread: SN75HVD07, SN75HVD06, SN75176A, THVD1500

  We are going to make a product for sale in series with 256 RS485 networked devices a 9600 bps, 4000 ft and half duplex. I read some topics about RS485 network here on the forum, but as I have no experience in this type of network I would like to take some questions. 

 The transceiver SN75HVD06P (10Mpbs; 1/8 unit load) integrated circuit which, according to the attached datasheet, works with up to 256 networked devices.
1) What if I use the model SN75HVD07P (1Mpbs; 1/8 unito load) I can't communicate at 9600 bps at 4000 ft? Because 1Mpbs < 9.6 Mbps?
2) SN75HVD06P Is this transceiver the most suitable for my application?

3) Can I use most popular SN75176B (up to 10 Mbps) ? Does it work by placing up to 256 devices on the same network and 4000 ft? 
4) I would like to know which is the best 4-way cable plus shield (2-way 24Vdc and GND, and 2-way communication) to make this RS485 half-duplex 9600 bps communication work at 4000ft (1.2km)?
5) Have you tested this network at 100 kbps at 4000 ft as some documents claim to work? Which cable did you use?

6) Do you have documents from these tests that you can share with us?

7) Or at least up to 57600 bps (57.6 kbps)? 

8) In this case the transceiver more indicated is SN65HVD7x half duplex family?
As we are going to buy this entire 4000 ft cable, I would not want to make a mistake in the purchase to do our tests, ensuring that the cable is correct and that my question is only the integrated circuits under test on the RS485 network.
Thank you very much for your valuable help in this matter.

Eng. Edemilso Ilha

  • 0
    TI__Mastermind 25705 points

    Edemilso,

    First of all, please check out this app note, in which many of your questions are addressed (especially section 9. Data Rate Versus Bus Length).

    1) At 9600bps, the communication distance is mainly limited by cable loss (resistive attenuation), not device's speed. Nevertheless SN75HVD07 works with this data rate (1Mbps >9600pbs).

    2) Other than speed and distance, is there any other requirement in the system? You can also check out the latest TI RS-485 in this e2e post.

    3) SN75HVD06, SN75HVD07, and SN75176B all would work, but the communication distance depends on the cable.

    4) Shielded twisted pair cable is recommended.

    5)6)7) please check out this app note for the data and cable type.

    8) 5V RS-485 is be preferred, generally have larger Vod. 

    Regards, 

  • 0 in reply to Hao L
    Prodigy 10 points

    Hello,

    Thank you for your help, I read the links.

    You asked me too:

    2) In addition to speed and distance, are there any other requirements in the system?

    Yes, the maximum number of 256 devices on the network, but this value can vary from 3 to 256.

    Taking these 5 factors into account:

    1) Up to 256 devices;

    2) 9600 bps;

    3) Half duplex;

    4) 4000 ft;

    5) And cable 2x22 AWG 120 W UTP

    I have 3 question:

    1) What is the least expensive IT transceiver that meets my needs?

    2) Will it be possible to use SN75176A (up to 5Mb> 9.6Kbps) for this application?

    3) How many devices on the network does it support? I looked for this information in his datasheet, but I didn't find it. Thanks for your answer.  

    Eng. Edemilso Ilha - Brazil

  • 0 in reply to Edemilso Ilha
    TI__Mastermind 25705 points

    Thanks for your information. Like I mentioned, I don't think the device choice would make much difference in this application, as long as it has 1/8 unit load (or ~96kOhm input resistance). SN75176A might not fit due to the 12kOhm resistance. THVD1500 may be the best choice cost wise.