dcs-bios.github.io/rs485-resistors.html at master · dcs-bios/dcs-bios.github.io · GitHub

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
<!DOCTYPE html>
<html>
  <body>
    <h1>RS-485 Resistor Calculator</h1>
    Using equations from <a href="http://www.ti.com/lit/an/slyt324/slyt324.pdf">RS-485: Passive failsafe for an idle bus</a> by Thomas Kugelstadt, Senior Applications Engineer at Texas Instruments.

    <h2>Step 1: Calculate R<sub>FS</sub></h2>

    Supply voltage: <input id="Vs" type="text" value="5"> V<br>
    Tolerance: <select id="Vs_tolerance">
      <option value="5">5%</option>
      <option value="10">10%</option>
    </select><br>
    Noise margin: <input id="mVnoise" type="text" value="50"> mV<br>
    R<sub>T1</sub>: <input id="R_T1" type="text" value="100"><br>
    For proper termination, use 100 ohm for Cat5 cable, 120 ohm for standard RS-485 cable. If your cable is short enough so you don't care about reflections, you can try higher values.<br><br>
    <button id="calc_RFS">Calculate R<sub>FS</sub></button>
    <div id="step1_output"></div>

    <h2>Step 2: Calculate R<sub>T2</sub></h2>
    R<sub>FS</sub>: <input id="R_FS" type="text"><br>
    <button id="calc_RT2">Calculate R<sub>T2</sub></button>
    <div id="step2_output"></div>

    <h2>Step 3: Determine max. number of devices</h2>
    R<sub>T2</sub>: <input id="R_T2" type="text"><br>
    <button id="calc_stats">Calculate</button><br>
    <div id="step3_output"></div>

    <script src="http://code.jquery.com/jquery-1.11.3.min.js"></script>
    <script src="rs485-resistors.js"></script>
  </body>
</html>