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i2cresistorcalculator.html
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<!DOCTYPE html>
<html lang="de">
<head>
<meta charset="UTF-8">
<meta name="musictohear" content="fee: zigarren im zeppelin">
<title>i2c Pullup Resistor Online Calculator</title>
<style>
body {
font-family: Verdana, sans-serif;
}
datalist {
display: block;
}
.inputdings {
display: grid;
grid-template-columns: repeat(4, min-content);
grid-template-rows: auto;
}
.inputdings label, .addendumdings label {
white-space: nowrap;
margin-right: 5px;
}
.inputdings div.dim, .addendumdings div.dim {
white-space: nowrap;
margin-left: 5px;
}
.inputdings div.comment {
font-family: Times, serif;
white-space: nowrap;
margin-left: 10px;
}
.inputdings div.comment .grid {
display: grid;
grid-template-columns: repeat(3, min-content);
grid-template-rows: repeat(2, min-content);
}
.inputdings div.comment .grid div {
border: 1px solid black;
padding: 4px;
text-align: right;
}
.selector {
display: grid;
grid-template-columns: repeat(2, min-content);
grid-template-rows: 1.1em;
}
.data span {
background: lightgray;
cursor: pointer;
}
.error {
background: red;
padding: 5px;
}
.result {
}
.addendumdings {
display: grid;
grid-template-columns: repeat(5, min-content);
grid-template-rows: auto;
}
.addmorebuttons {
margin-top: 10px;
}
.addmorebuttons span {
background: lightgray;
cursor: pointer;
}
.addremove span {
background: lightgray;
cursor: pointer;
}
.addremove {
margin-left: 10px;
}
#baseresistor .addremove {
display: none;
}
.addedresistors .addremove span {
background: lightgray;
cursor: pointer;
}
.realworlddata {
display: grid;
grid-template-columns: repeat(2, min-content);
grid-template-rows: 1.1em;
}
.realworlddata div {
margin-left: 10px;
}
.headtitle {
color: blue;
margin-bottom: 0px;
}
.headresult {
color: lightblue;
margin-bottom: 0px;
}
</style>
<script>
function divvalue(thediv, theinput) {
theinput = document.getElementById(theinput);
var content = thediv.getAttribute("data-value");
theinput.value = content;
calculate();
}
function displayError(msg) {
document.getElementById('result').innerHTML = '<span class="error">' + msg + '</span>';
}
function getValue(id, errormsg) {
var element = document.getElementById(id);
var val = Number(element.value);
if (isNaN(val)) {
displayError(errormsg);
return -1;
}
return val;
}
function iolcheck() {
var vcc = getValue('vcc', "V<sub>cc</sub> is not a number");
if (vcc<=2.0) {
document.getElementById('iol').value="2";
} else {
document.getElementById('iol').value="3";
}
}
var addcounter = 1;
function calculateadditionalresistorsvalue() {
var r = 0, i;
for (i=0; i<addcounter; i++) {
var group = document.getElementById('resistors'+i);
var rr = group.getElementsByTagName('input');
if (rr.length==1) {
var rvs = rr[0].value;
var rv = Number(rvs);
if ( (rv!=0) && (! isNaN(rv)) ) {
if (r==0) {
r = rv;
} else {
r = 1/(1/r+1/rv);
}
} else {
document.getElementById('addendumresult').innerHTML =
'<span class="error">'+
'An additional resistor value is not a number.'+
'</span>';
return -1;
}
}
}
return r;
}
function calculate() {
var vcc = getValue('vcc', "V<sub>cc</sub> is not a number");
if (vcc<0) return;
var tr = getValue('tr', "t<sub>r</sub> is not a number");
if (tr<0) return;
var cb = getValue('cb', "C<sub>b</sub> is not a number");
if (cb<0) return;
var vol = 0;
if (document.getElementById('vol').value=='0.2*Vcc') {
vol=0.2*vcc;
} else {
vol = getValue('vol', "V<sub>OL</sub> is not a number");
if (vol<0) return;
}
var iol= getValue('iol', "I<sub>OL</sub> is not a number");
if (iol<0) return;
var rp1 = (tr) / (0.8473 * cb * 0.001);
var rp2 = (vcc - vol) / (iol * 0.001);
var rpmax = 0, rpmin = 0;
if (rp1<rp2) {
rpmax = rp2; rpmin = rp1;
} else {
rpmax = rp1; rpmin = rp2;
}
var rpmaxs =
'R<sub>p</sub>(max) = ' + Math.round(rpmax * 100) / 100 + ' Ω';
var rpmins =
'R<sub>p</sub>(min) = ' + Math.round(rpmin * 100) / 100 + ' Ω';
document.getElementById('result').innerHTML =
'We can select any available resistor value between '+rpmins+' and '+
rpmaxs+'.<br>The value of the pullup resistor can be selected based on the '+
'trade-off for the power consumption and speed.';
// 1/rg = 1/r1 + 1/r2; --> 1/rg-1/r2 = 1/r1 --> r1 = 1/(1/rg-1/r2)
var addedresis = calculateadditionalresistorsvalue();
if (addedresis>0) {
var addedresiss =
'R<sub>Addsum</sub> = ' + Math.round(addedresis * 100) / 100 + ' Ω';
var rpmaxadd = 1/(1/rpmax - 1/addedresis);
var rpminadd = 1/(1/rpmin - 1/addedresis);
var rpmaxadds =
'R<sub>pAdd</sub>(max) = ' + Math.round(rpmaxadd * 100) / 100 + ' Ω';
var rpminadds =
'R<sub>pAdd</sub>(min) = ' + Math.round(rpminadd * 100) / 100 + ' Ω';
if (addedresis<rpmax) {
if (addedresis<rpmin) {
document.getElementById('addendumresult').innerHTML =
"Your already existing resistor sum "+addedresiss+" is to low!";
} else {
document.getElementById('addendumresult').innerHTML = "You could add "+rpminadds+" or more.";
}
} else {
document.getElementById('addendumresult').innerHTML =
'Existing resistor sum is '+addedresiss+'. Select the remaining resistor value between '+rpminadds+' and '+
rpmaxadds+'.';
}
}
}
function addresistor() {
var base = document.getElementById('baseresistor');
var bases = base.innerHTML.replace("(0)","("+addcounter+")");
var divnode = document.createElement("DIV");
divnode.id = "resistors"+addcounter;
divnode.innerHTML = bases;
document.getElementById('addedresistors').appendChild(divnode);
addcounter++;
}
function removeresistor(param) {
document.getElementById('resistors'+param).innerHTML="";
}
window.onload=calculate;
</script>
</head>
<body>
<div class="calculator">
<h2 class="headtitle">i2c Pullup Resistor Online Calculator</h2>
<div class="inputdings">
<!-- Vcc -->
<label for="vcc">V<sub>cc</sub>:</label>
<div>
<input type="text" id="vcc" name="vcc" value="3.3" size="5"
onChange="iolcheck(); calculate();" onKeyup="iolcheck(); calculate();">
</div>
<div class="dim">V</div>
<div class="comment">
<div>Supply rail voltage</div>
<div class="grid">
<div class="data" onClick="divvalue(this, 'vcc'); iolcheck();" data-value="3.3"><span>3.3 V</span></div>
<div class="data" onClick="divvalue(this, 'vcc'); iolcheck();" data-value="5.0"><span>5.0 V</span></div>
</div>
</div>
<!-- tr -->
<label for="vcc">t<sub>r</sub>:</label>
<div>
<input type="text" id="tr" name="tr" value="1000" size="5"
onChange="calculate();" onKeyup="calculate();">
</div>
<div class="dim">ns</div>
<div class="comment">
<div>Maximal rise time of both SDA and SCL signals</div>
<div class="grid">
<div>Standard Mode<br><small>f<sub>scl</sub> = 100 kHz</small></div>
<div>Fast Mode<br><small>f<sub>scl</sub> = 400 kHz</small></div>
<div>Fast Mode Plus<br><small>f<sub>scl</sub> = 1000 kHz</small></div>
<div class="data" onClick="divvalue(this, 'tr')" data-value="1000"><span>1000 ns</span></div>
<div class="data" onClick="divvalue(this, 'tr')" data-value="300"><span>300 ns</span></div>
<div class="data" onClick="divvalue(this, 'tr')" data-value="120"><span>120 ns</span></div>
</div>
</div>
<!-- cb -->
<label for="cb">C<sub>b</sub>:</label>
<div>
<input type="text" id="cb" name="cb" value="400" size="5"
onChange="calculate();" onKeyup="calculate();">
</div>
<div class="dim">pF</div>
<div class="comment">
<div>Maximal capacitive load for each bus line</div>
<div class="grid">
<div>Standard Mode</div>
<div>Fast Mode</div>
<div>Fast Mode Plus</div>
<div class="data" onClick="divvalue(this, 'cb')" data-value="400"><span>400 pF</span></div>
<div class="data" onClick="divvalue(this, 'cb')" data-value="400"><span>400 pF</span></div>
<div class="data" onClick="divvalue(this, 'cb')" data-value="550"><span>550 pF</span></div>
</div>
Some real world data:
<div class="realworlddata">
<div>FR4</div>
<div>C ~ 0.7 pF/cm</div>
<div></div>
<div>C ~ 1.3 pF/cm at 50 Ω</div>
<div>Coax</div>
<div>C ~ 1 pF/cm at 50 Ω</div>
<div>PCF8574</div>
<div>C < 7 pF/pin</div>
<div>ATTINY85</div>
<div>C = 14 pF/pin</div>
<div>ATMEGA328p</div>
<div>C = 10 pF/pin</div>
<div>ESP8266</div>
<div>C = 2 pF/pin</div>
<div>ESP32</div>
<div>C = 2 pF/pin</div>
</div>
</div>
<!--
-->
<!-- Vol -->
<label for="vol">V<sub>OL</sub>:</label>
<div>
<input type="text" id="vol" name="vol" value="0.4" size="5"
onChange="calculate();" onKeyup="calculate();">
</div>
<div class="dim">V</div>
<div class="comment">
<div>The V<sub>OL</sub> level can be read as a valid logical</div>
<div>low by the input buffers of an IC.</div>
<div class="grid">
<div>Standard Mode</div>
<div>Fast Mode</div>
<div>Fast Mode Plus</div>
<div class="data" onClick="divvalue(this, 'vol')" data-value="0.4"><span>0.4 V</span></div>
<div class="data" onClick="divvalue(this, 'vol')" data-value="0.4"><span>0.4 V</span></div>
<div class="data" onClick="divvalue(this, 'vol')" data-value="0.4"><span>0.4 V</span></div>
<div class="data" onClick="divvalue(this, 'vol')" data-value=""><span></span></div>
<div class="data" onClick="divvalue(this, 'vol')" data-value="0.2*Vcc"><span>0.2 * V<sub>cc</sub></span></div>
<div class="data" onClick="divvalue(this, 'vol')" data-value="0.2*Vcc"><span>0.2 * V<sub>cc</sub></span></div>
</div>
</div>
<!-- Iol -->
<label for="vol">I<sub>OL</sub>:</label>
<div>
<input type="text" id="iol" name="iol" value="3" size="5"
onChange="calculate();" onKeyup="calculate();">
</div>
<div class="dim">mA</div>
<div class="comment">
<div>I<sub>OL</sub> is defined as V<sub>cc</sub> > 2 V: 3 mA, V<sub>cc</sub> ≤ 2 V: 2 mA</div>
</div>
</div>
<h2 class="headresult">Results</h2>
<div class="result">
<div id="result">Gra!!!</div>
</div>
<hr>
<h2 class="headtitle">include existing Resistors</h2>
<div id="resistors0">
<div id="baseresistor">
<div class="addendumdings">
<label for="vol">R:</label>
<div>
<input type="text" value="10000" size="6"
onChange="calculate();" onKeyup="calculate();">
</div>
<div class="dim">Ω</div>
<div class="addremove"><span onClick="removeresistor(0); calculate();">Remove</span></div>
</div>
</div>
</div>
</div>
<div id="addedresistors">
</div>
<div class="addmorebuttons">
<span onClick="addresistor(); calculate();">Add another resistor</span>
</div>
<h2 class="headresult">Results</h2>
<div class="addendumresult">
<div id="addendumresult">Gra!!!</div>
</div>
<hr>
<div class="reference">
<h3>References</h3>
<ul>
<li>
<a
href="https://www.ti.com/lit/an/slva689/slva689.pdf?ts=1604288051277&ref_url=https%253A%252F%252Fwww.google.com%252F">Texas Instruments<br>
Application Report SLVA689 – February 2015<br>
I2C Bus Pullup Resistor Calculation</a>
</li>
<li>
<a
href="https://www.nxp.com/docs/en/user-guide/UM10204.pdf">
NXP Semiconductors<br>
UM10204<br>
I2C-bus specification and user manual<br>
Rev. 6 — 4 April 2014 User manual</a>
</li>
</ul>
</div>
<div class="author">
<h4>Author</h4>
Holger Lembke
</div>
</body>
</html>