# Modbus 16 bit registers to Float value

**URL:** <https://discourse.nodered.org/t/modbus-16-bit-registers-to-float-value/72784>\
**Category:** General\
**Tags:** function-node\
**Created:** [27 December 2022 19:49 UTC](https://discourse.nodered.org/t/modbus-16-bit-registers-to-float-value/72784 "2022-12-27T19:49:53Z")\
**Posts on this page:** 6\
**Page:** 1

<div class="post-metadata">

**Author:** ![thutchis](https://avatars.discourse-cdn.com/v4/letter/t/9fc348/32.png) [@thutchis](https://discourse.nodered.org/u/thutchis)\
**Post date:** [27 December 2022 19:49 UTC](https://discourse.nodered.org/t/modbus-16-bit-registers-to-float-value/72784/1 "2022-12-27T19:49:53Z")

</div>

I am NOT a javascript programmer, just trying to read a Modbus device and get a value out to inject into a data base. I have been struggling with this for hours and hours reading this forum and others.

I get two 16 bit unsigned integers in the msg.payload from Modbus-Flex-Getter [61124, 17011] I put them into a function node with the following code:

```auto
let pay = msg.payload;

const buf = Buffer.allocUnsafe(4);
buf.writeUInt16BE(pay[0], 2);
buf.writeUInt16BE(pay[1], 0);
msg.payload = buf.readFloatBE(0);

return msg;

```

The value returned in a debug node from the function node is the correct value, but in hex code (0x3c.fbb1). When I use a change node to create a flow variable from the value, I get a ",undefined) : msg.topic : string[73]" error. How do I get a numeric float value (61.642425537109375) from the hex code returned?

---

<div class="post-metadata">

**Author:** ![Becker](https://avatars.discourse-cdn.com/v4/letter/b/c77e96/32.png) [@Becker](https://discourse.nodered.org/u/Becker)\
**Post date:** [27 December 2022 20:23 UTC](https://discourse.nodered.org/t/modbus-16-bit-registers-to-float-value/72784/2 "2022-12-27T20:23:07Z")

</div>

Hi, just use the buffer parser and you´ll get success soon.

edit, I tried:

```auto
[
    {
        "id": "11026c1822d2eaa3",
        "type": "inject",
        "z": "9f6752b0.b55988",
        "name": "",
        "props": [
            {
                "p": "payload"
            }
        ],
        "repeat": "",
        "crontab": "",
        "once": false,
        "onceDelay": 0.1,
        "topic": "",
        "payload": "true",
        "payloadType": "bool",
        "x": 1690,
        "y": 140,
        "wires": [
            [
                "9b37eb3980bfca78"
            ]
        ]
    },
    {
        "id": "9b37eb3980bfca78",
        "type": "function",
        "z": "9f6752b0.b55988",
        "name": "Array",
        "func": "msg.payload = [61124,17011];\nreturn msg;",
        "outputs": 1,
        "noerr": 0,
        "initialize": "",
        "finalize": "",
        "libs": [],
        "x": 1690,
        "y": 200,
        "wires": [
            [
                "81d3c91a381f1cf9"
            ]
        ]
    },
    {
        "id": "97b1d3916ce91a4f",
        "type": "debug",
        "z": "9f6752b0.b55988",
        "name": "debug 2",
        "active": true,
        "tosidebar": true,
        "console": false,
        "tostatus": false,
        "complete": "false",
        "statusVal": "",
        "statusType": "auto",
        "x": 1700,
        "y": 320,
        "wires": []
    },
    {
        "id": "81d3c91a381f1cf9",
        "type": "buffer-parser",
        "z": "9f6752b0.b55988",
        "name": "",
        "data": "payload",
        "dataType": "msg",
        "specification": "spec",
        "specificationType": "ui",
        "items": [
            {
                "type": "uint16be",
                "name": "item1",
                "offset": 0,
                "length": 1,
                "offsetbit": 0,
                "scale": "1",
                "mask": ""
            }
        ],
        "swap1": "",
        "swap2": "",
        "swap3": "",
        "swap1Type": "swap",
        "swap2Type": "swap",
        "swap3Type": "swap",
        "msgProperty": "payload",
        "msgPropertyType": "str",
        "resultType": "keyvalue",
        "resultTypeType": "return",
        "multipleResult": false,
        "fanOutMultipleResult": false,
        "setTopic": true,
        "outputs": 1,
        "x": 1710,
        "y": 260,
        "wires": [
            [
                "97b1d3916ce91a4f"
            ]
        ]
    }
]

```

and got 61124 🧐

@Steve-Mcl will know

---

<div class="post-metadata">

**Author:** ![thutchis](https://avatars.discourse-cdn.com/v4/letter/t/9fc348/32.png) [@thutchis](https://discourse.nodered.org/u/thutchis)\
**Post date:** [27 December 2022 20:40 UTC](https://discourse.nodered.org/t/modbus-16-bit-registers-to-float-value/72784/3 "2022-12-27T20:40:13Z")

</div>

I have tried every possible combination of the buffer-parser without a usable value.

 ![image](https://us1.discourse-cdn.com/flex026/uploads/nodered/original/3X/b/c/bceadf227ea4520c96f460e4fb6c133377196df9.png)

I get an array[1] of 0x0.0f44276 or another useless number.

---

<div class="post-metadata">

**Author:** ![Steve-Mcl](https://sea2.discourse-cdn.com/flex026/user_avatar/discourse.nodered.org/steve-mcl/32/4826_2.png) [@Steve-Mcl](https://discourse.nodered.org/u/Steve-Mcl)\
**Post date:** [28 December 2022 19:09 UTC](https://discourse.nodered.org/t/modbus-16-bit-registers-to-float-value/72784/5 "2022-12-28T19:09:35Z")

</div>

> [@thutchis](#):
>
> I get two 16 bit unsigned integers in the msg.payload from Modbus-Flex-Getter [61124, 17011]

> [@thutchis](#):
>
> How do I get a numeric float value (61.642425537109375) from the hex code returned?

You dont, you get `60.98316955566406` (you really should be exact when asking for assistance.)

Anyhow, I can see from your function code your data is 32bit, then 16bit swapped then read as a Big Endian value. Which is odd - what writes the values to ModBus registers in the first place?

No-code solution...

 ![image](https://us1.discourse-cdn.com/flex026/uploads/nodered/original/3X/f/b/fbdbce1a2a85dbb0ef1ded0bd1bee7361671debc.png)

 ![image](https://us1.discourse-cdn.com/flex026/uploads/nodered/original/3X/c/d/cd49efab0cbec7f7d263e8937df28cebb6746173.png)

Demo flow (use `CTRL-I` to import)

```auto
[{"id":"d91ff976927ea647","type":"buffer-parser","z":"22bb2f33123bf539","name":"swap 32, swap16, BE","data":"payload","dataType":"msg","specification":"spec","specificationType":"ui","items":[{"type":"floatbe","name":"temperature","offset":0,"length":1,"offsetbit":0,"scale":"1","mask":""}],"swap1":"swap32","swap2":"swap16","swap3":"","swap1Type":"swap","swap2Type":"swap","swap3Type":"swap","msgProperty":"payload","msgPropertyType":"str","resultType":"keyvalue","resultTypeType":"return","multipleResult":false,"fanOutMultipleResult":false,"setTopic":true,"outputs":1,"x":760,"y":260,"wires":[["339f476ae7d0e70e"]]},{"id":"b0d077567a7af96f","type":"inject","z":"22bb2f33123bf539","name":"","props":[{"p":"payload"},{"p":"topic","vt":"str"}],"repeat":"","crontab":"","once":false,"onceDelay":0.1,"topic":"","payload":"[61124, 17011]","payloadType":"json","x":520,"y":300,"wires":[["d91ff976927ea647","dbccc077e654fd40"]]},{"id":"339f476ae7d0e70e","type":"debug","z":"22bb2f33123bf539","name":"debug 153","active":true,"tosidebar":true,"console":false,"tostatus":false,"complete":"false","statusVal":"","statusType":"auto","x":970,"y":260,"wires":[]},{"id":"dbccc077e654fd40","type":"function","z":"22bb2f33123bf539","name":"function 4","func":"let pay = msg.payload;\n\nconst buf = Buffer.allocUnsafe(4);\nbuf.writeUInt16BE(pay[0], 2);\nbuf.writeUInt16BE(pay[1], 0);\nmsg.payload = buf.readFloatBE(0);\n\nreturn msg;\n","outputs":1,"noerr":0,"initialize":"","finalize":"","libs":[],"x":720,"y":340,"wires":[["67a7553fc6f4235f"]]},{"id":"67a7553fc6f4235f","type":"debug","z":"22bb2f33123bf539","name":"debug 155","active":true,"tosidebar":true,"console":false,"tostatus":false,"complete":"false","statusVal":"","statusType":"auto","x":970,"y":340,"wires":[]}]

```

---

<div class="post-metadata">

**Author:** ![thutchis](https://avatars.discourse-cdn.com/v4/letter/t/9fc348/32.png) [@thutchis](https://discourse.nodered.org/u/thutchis)\
**Post date:** [28 December 2022 20:14 UTC](https://discourse.nodered.org/t/modbus-16-bit-registers-to-float-value/72784/6 "2022-12-28T20:14:21Z")

</div>

Thank you for your help. I never would have figured out how exactly to use the buffer-parse node.

To answer your question. The modbus registers are read from the the floating point addresses of a AutomationDirect CLICK PLC and are 4-20ma analog inputs.

---

<div class="post-metadata">

**Author:** ![system](https://us1.discourse-cdn.com/flex026/uploads/nodered/original/1X/d073cd938eafa2e558d7c2cd59003b3ef4963033.png) [@system](https://discourse.nodered.org/u/system)\
**Post date:** [11 January 2023 20:14 UTC](https://discourse.nodered.org/t/modbus-16-bit-registers-to-float-value/72784/7 "2023-01-11T20:14:47Z")

</div>

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