CRC16 modbus rtu

README.md

Funtion block that adds CRC 16 checksum to modbus rtu command. Example:

input: 010600010100 output: 010600010100D99A

flow.json

[{"id":"e6126f89.fbab88","type":"tab","label":"modbus rtu crc","disabled":false,"info":""},{"id":"7812b725.54f17","type":"function","z":"e6126f89.fbab88","name":"CRC16-modbus","func":"var CRCMaster = {\n    StringToCheck: \"\",\n    CleanedString: \"\",\n    CRCTableDNP: [],\n    init: function() {\n        this.CRCDNPInit();\n    },\n    CleanString: function(inputType) {\n        if (inputType == \"ASCII\") {\n            this.CleanedString = this.StringToCheck;\n        } else {\n            if (this.StringToCheck.match(/^[0-9A-F \\t]+$/gi) !== null) {\n                this.CleanedString = this._hexStringToString(this.StringToCheck.toUpperCase().replace(/[\\t ]/g, ''));\n            } else {\n                window.alert(\"String doesn't seem to be a valid Hex input.\");\n                return false;\n            }\n        }\n        return true;\n    },\n    CRCDNPInit: function() {\n        var i, j, crc, c;\n        for (i = 0; i < 256; i++) {\n            crc = 0;\n            c = i;\n            for (j = 0; j < 8; j++) {\n                if ((crc ^ c) & 0x0001) crc = (crc >> 1) ^ 0xA6BC;\n                else crc = crc >> 1;\n                c = c >> 1;\n            }\n            this.CRCTableDNP[i] = crc;\n        }\n    },\n    CRC16Modbus: function() {\n        var crc = 0xFFFF;\n        var str = this.CleanedString;\n        for (var pos = 0; pos < str.length; pos++) {\n            crc ^= str.charCodeAt(pos);\n            for (var i = 8; i !== 0; i--) {\n                if ((crc & 0x0001) !== 0) {\n                    crc >>= 1;\n                    crc ^= 0xA001;\n                } else\n                    crc >>= 1;\n            }\n        }\n        return crc;\n    },\n    _stringToBytes: function(str) {\n        var ch, st, re = [];\n        for (var i = 0; i < str.length; i++) {\n            ch = str.charCodeAt(i); // get char\n            st = []; // set up \"stack\"\n            do {\n                st.push(ch & 0xFF); // push byte to stack\n                ch = ch >> 8; // shift value down by 1 byte\n            }\n            while (ch);\n            // add stack contents to result\n            // done because chars have \"wrong\" endianness\n            re = re.concat(st.reverse());\n        }\n        // return an array of bytes\n        return re;\n    },\n    _hexStringToString: function(inputstr) {\n        var hex = inputstr.toString(); //force conversion\n        var str = '';\n        for (var i = 0; i < hex.length; i += 2)\n            str += String.fromCharCode(parseInt(hex.substr(i, 2), 16));\n        return str;\n    },\n    Calculate: function(str, inputType) {\n        this.StringToCheck = str;\n        if (this.CleanString(inputType)) {\n            crcinputcrc16modbus=this.CRC16Modbus().toString(16).toUpperCase();\n            crcinputcrc16modbus=crcinputcrc16modbus.substr(2) + crcinputcrc16modbus.substr(0, 2); //swap bytes\n   \n        }\n    }\n};\n\nCRCMaster.init();\n\nvar inputType = \"HEX\";\nvar crcinputcrc16modbus;\nvar crcinput = msg.payload;\n\nCRCMaster.Calculate(crcinput, inputType);\n\nmsg.payload = crcinput + crcinputcrc16modbus;\n\nreturn msg;","outputs":1,"noerr":0,"initialize":"","finalize":"","x":660,"y":380,"wires":[["da260a66.2e0fb"]]},{"id":"265c58e5.dc37a","type":"inject","z":"e6126f89.fbab88","name":"","props":[{"p":"payload"}],"repeat":"","crontab":"","once":false,"onceDelay":0.1,"topic":"","payload":"010600010100","payloadType":"str","x":400,"y":380,"wires":[["7812b725.54f17"]]},{"id":"da260a66.2e0fb","type":"debug","z":"e6126f89.fbab88","name":"","active":true,"tosidebar":true,"console":false,"tostatus":false,"complete":"false","statusVal":"","statusType":"auto","x":900,"y":380,"wires":[]}]

I'm interested in your node, do you thing it's possible to start from a string, let's say QPIGS, convert it to hexa, which gives 5150494753 and then calculate the CRC16 on this hexa value, which makes B7A9, so a buffer in hexa of 5150494753B7A9 or in decimal for the node change [81,80,73,71,83,183,169,13] ?
Thanks for your answer

I'm interested in your node, do you thing it's possible to start from a string, let's say QPIGS, convert it to hexa, which gives 5150494753 and then calculate the CRC16 on this hexa value, which makes B7A9, so a buffer in hexa of 5150494753B7A9 or in decimal for the node change [81,80,73,71,83,183,169,13] ?
Thanks for your answer

Hi, I don't know, what is QPIGS.

QPIGS is a word an inverter can understand.
There are many others in the protocol used by these machines.
It must be sent by the Serial node of NR via the serial port in rs232.
But you have to calculate its CRC and add it to the end of the buffer.
For the moment, I have calculated this statically by hand. Is it possible to pass this QPIGS string or another ;-) to your CRC16-modbus function node so that this CRC is created on demand and not statically and therefore added at the end of the buffer (in my example the CRC gave B7A9)
Here is an example of what I need to be able to send in NR.

The check code obtained is：2DC1 ，How can I get this result：2D C1 ？Thx！