# Converting an array of bytes into a int16 to write in a modbus server(holding register)

**URL:** <https://discourse.nodered.org/t/converting-an-array-of-bytes-into-a-int16-to-write-in-a-modbus-server-holding-register/62370>\
**Category:** General\
**Created:** [8 May 2022 14:47 UTC](https://discourse.nodered.org/t/converting-an-array-of-bytes-into-a-int16-to-write-in-a-modbus-server-holding-register/62370 "2022-05-08T14:47:03Z")\
**Posts on this page:** 20\
**Page:** 1

<div class="post-metadata">

**Author:** ![Theodros](https://sea2.discourse-cdn.com/flex026/user_avatar/discourse.nodered.org/theodros/32/61068_2.png) [@Theodros](https://discourse.nodered.org/u/Theodros)\
**Post date:** [8 May 2022 14:47 UTC](https://discourse.nodered.org/t/converting-an-array-of-bytes-into-a-int16-to-write-in-a-modbus-server-holding-register/62370/1 "2022-05-08T14:47:03Z")

</div>

Hello guys,

I'm trying to convert an array of bytes(16bytes exactly) that I'm receiving from a function to an int16 to be able to enter it in a modbus holding register but I don't understand how to convert it. I tried with the buffer parser and it didn't work (might be that don't know how to use it).

Important Info: I must absolutely do the conversion from this array

Do you know a way to do the conversion?

An example of what I want to be able to do:

 ![image](https://us1.discourse-cdn.com/flex026/uploads/nodered/original/3X/6/d/6dcad394bc05cd36380cae04d8aa196f38b7b440.png)

---

<div class="post-metadata">

**Author:** ![marcus-j-davies](https://sea2.discourse-cdn.com/flex026/user_avatar/discourse.nodered.org/marcus-j-davies/32/103435_2.png) [@marcus-j-davies](https://discourse.nodered.org/u/marcus-j-davies)\
**Post date:** [8 May 2022 15:01 UTC](https://discourse.nodered.org/t/converting-an-array-of-bytes-into-a-int16-to-write-in-a-modbus-server-holding-register/62370/2 "2022-05-08T15:01:20Z")

</div>

The node you will need courtesy of @Steve-Mcl

> **[node-red-contrib-buffer-parser](https://flows.nodered.org/node/node-red-contrib-buffer-parser)**
>
> Node-red nodes to convert values to and from buffer/array. Supports Big/Little Endian, BCD, byte swapping and much more

Have not used this node myself, but seems to be the goto for this requirement

---

<div class="post-metadata">

**Author:** ![Theodros](https://sea2.discourse-cdn.com/flex026/user_avatar/discourse.nodered.org/theodros/32/61068_2.png) [@Theodros](https://discourse.nodered.org/u/Theodros)\
**Post date:** [8 May 2022 15:04 UTC](https://discourse.nodered.org/t/converting-an-array-of-bytes-into-a-int16-to-write-in-a-modbus-server-holding-register/62370/3 "2022-05-08T15:04:43Z")

</div>

I might be really dumb but i tried to use it multiple times looking throught the forums and tutorials but I didn't manage to make it work

---

<div class="post-metadata">

**Author:** ![Theodros](https://sea2.discourse-cdn.com/flex026/user_avatar/discourse.nodered.org/theodros/32/61068_2.png) [@Theodros](https://discourse.nodered.org/u/Theodros)\
**Post date:** [8 May 2022 15:08 UTC](https://discourse.nodered.org/t/converting-an-array-of-bytes-into-a-int16-to-write-in-a-modbus-server-holding-register/62370/4 "2022-05-08T15:08:33Z")

</div>

This what I have when I use It:

 ![image](https://us1.discourse-cdn.com/flex026/uploads/nodered/original/3X/8/8/88091f46814eb4578d92701971224a331fa2bfa1.png)

I don't understand the parameters

---

<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:** [8 May 2022 15:11 UTC](https://discourse.nodered.org/t/converting-an-array-of-bytes-into-a-int16-to-write-in-a-modbus-server-holding-register/62370/5 "2022-05-08T15:11:31Z")

</div>

> [@Theodros](#):
>
> I don't understand the parameters

 ![image](https://us1.discourse-cdn.com/flex026/uploads/nodered/original/3X/a/d/ad15bf28118b86985776923ef65f735f47c80670.png)

---

<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:** [8 May 2022 15:12 UTC](https://discourse.nodered.org/t/converting-an-array-of-bytes-into-a-int16-to-write-in-a-modbus-server-holding-register/62370/6 "2022-05-08T15:12:25Z")

</div>

> [@Theodros](#):
>
> I don't understand the parameters

What does the input data look like and what do you expect out of it?

PS, for modbus, you likely need UINT16be not INT16be

---

<div class="post-metadata">

**Author:** ![Theodros](https://sea2.discourse-cdn.com/flex026/user_avatar/discourse.nodered.org/theodros/32/61068_2.png) [@Theodros](https://discourse.nodered.org/u/Theodros)\
**Post date:** [8 May 2022 15:20 UTC](https://discourse.nodered.org/t/converting-an-array-of-bytes-into-a-int16-to-write-in-a-modbus-server-holding-register/62370/7 "2022-05-08T15:20:40Z")

</div>

So here's my flow

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    },
    {
        "id": "5fc121eeade2156a",
        "type": "change",
        "z": "1378ba83.90c825",
        "name": "",
        "rules": [
            {
                "t": "set",
                "p": "selected",
                "pt": "flow",
                "to": "payload",
                "tot": "msg"
            }
        ],
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        "property": "",
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        "to": "",
        "reg": false,
        "x": 1200,
        "y": 1000,
        "wires": [
            []
        ]
    },
    {
        "id": "5676a3cd7ef5e23d",
        "type": "join",
        "z": "1378ba83.90c825",
        "name": "",
        "mode": "custom",
        "build": "object",
        "property": "payload",
        "propertyType": "msg",
        "key": "topic",
        "joiner": "\\n",
        "joinerType": "str",
        "accumulate": true,
        "timeout": "",
        "count": "1",
        "reduceRight": false,
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        "reduceInitType": "",
        "reduceFixup": "",
        "x": 1010,
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                "5fc121eeade2156a"
            ]
        ]
    },
    {
        "id": "3ffeefaa5596a04c",
        "type": "debug",
        "z": "1378ba83.90c825",
        "name": "",
        "active": true,
        "tosidebar": true,
        "console": false,
        "tostatus": false,
        "complete": "payload",
        "targetType": "msg",
        "statusVal": "",
        "statusType": "auto",
        "x": 810,
        "y": 1400,
        "wires": []
    },
    {
        "id": "8d613ded2d4ecc2e",
        "type": "ui_button",
        "z": "1378ba83.90c825",
        "name": "",
        "group": "671cb6d0f0a7d1c7",
        "order": 1,
        "width": 0,
        "height": 0,
        "passthru": false,
        "label": "Valider",
        "tooltip": "",
        "color": "",
        "bgcolor": "",
        "className": "",
        "icon": "",
        "payload": "",
        "payloadType": "date",
        "topic": "topic",
        "topicType": "msg",
        "x": 190,
        "y": 1280,
        "wires": [
            [
                "e72aa291dd82fd34"
            ]
        ]
    },
    {
        "id": "19f79ff39da8bb1b",
        "type": "buffer-parser",
        "z": "1378ba83.90c825",
        "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",
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        "msgProperty": "payload",
        "msgPropertyType": "str",
        "resultType": "keyvalue",
        "resultTypeType": "return",
        "multipleResult": false,
        "fanOutMultipleResult": false,
        "setTopic": true,
        "outputs": 1,
        "x": 630,
        "y": 1400,
        "wires": [
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                "3ffeefaa5596a04c"
            ]
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    },
    {
        "id": "671cb6d0f0a7d1c7",
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        "name": "Requête 1",
        "tab": "3f071cb9a3d49f7f",
        "order": 1,
        "disp": true,
        "width": "6",
        "collapse": false,
        "className": ""
    },
    {
        "id": "ac5f4946e8c230e7",
        "type": "ui_group",
        "name": "Initialisation des listes déroulantes",
        "tab": "3f071cb9a3d49f7f",
        "order": 4,
        "disp": true,
        "width": "6",
        "collapse": false,
        "className": ""
    },
    {
        "id": "846c632af12c3e74",
        "type": "ui_group",
        "name": "Requête 2",
        "tab": "3f071cb9a3d49f7f",
        "order": 1,
        "disp": true,
        "width": "6",
        "collapse": false,
        "className": ""
    },
    {
        "id": "25e2db2699b87ee1",
        "type": "ui_group",
        "name": "Requête 3",
        "tab": "3f071cb9a3d49f7f",
        "order": 3,
        "disp": true,
        "width": "6",
        "collapse": false,
        "className": ""
    },
    {
        "id": "3f071cb9a3d49f7f",
        "type": "ui_tab",
        "name": "COMPRESSEUR",
        "icon": "COMPRESSEUR",
        "disabled": false,
        "hidden": false
    }
]

```

---

<div class="post-metadata">

**Author:** ![Theodros](https://sea2.discourse-cdn.com/flex026/user_avatar/discourse.nodered.org/theodros/32/61068_2.png) [@Theodros](https://discourse.nodered.org/u/Theodros)\
**Post date:** [8 May 2022 15:23 UTC](https://discourse.nodered.org/t/converting-an-array-of-bytes-into-a-int16-to-write-in-a-modbus-server-holding-register/62370/8 "2022-05-08T15:23:46Z")

</div>

I'm inputing data from the dashboard as a number (0 or 1) and putting it inside a first array going from 0 to 79. Then from this array, I extract 16 numbers that i put inside another array to then convert it into an UINT16be  
(I don't know if It's clear)

---

<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:** [8 May 2022 15:28 UTC](https://discourse.nodered.org/t/converting-an-array-of-bytes-into-a-int16-to-write-in-a-modbus-server-holding-register/62370/9 "2022-05-08T15:28:58Z")

</div>

Show me what the data in flow.selected looks like.

Better still, copy some actual input data (using the copy value button)  
 ![image](https://us1.discourse-cdn.com/flex026/uploads/nodered/original/3X/d/8/d8b1ec40e896fdc450ad00f0e6695f26379715b4.png)

Then explain what that data should be.

e.g. if you show my flow.selected has [1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16] what should it look like before it goes to modbus?

---

<div class="post-metadata">

**Author:** ![Theodros](https://sea2.discourse-cdn.com/flex026/user_avatar/discourse.nodered.org/theodros/32/61068_2.png) [@Theodros](https://discourse.nodered.org/u/Theodros)\
**Post date:** [8 May 2022 15:29 UTC](https://discourse.nodered.org/t/converting-an-array-of-bytes-into-a-int16-to-write-in-a-modbus-server-holding-register/62370/10 "2022-05-08T15:29:14Z")

</div>

- The first problem might be that I'm inputing numbers in the array (wich are already integer if i'm not wrong), but than how do I feel up my first array with boolean numbers

---

<div class="post-metadata">

**Author:** ![Theodros](https://sea2.discourse-cdn.com/flex026/user_avatar/discourse.nodered.org/theodros/32/61068_2.png) [@Theodros](https://discourse.nodered.org/u/Theodros)\
**Post date:** [8 May 2022 15:31 UTC](https://discourse.nodered.org/t/converting-an-array-of-bytes-into-a-int16-to-write-in-a-modbus-server-holding-register/62370/11 "2022-05-08T15:31:04Z")

</div>

Here's how it looks like

{"S1":0,"B1":1}

![image](https://us1.discourse-cdn.com/flex026/uploads/nodered/original/3X/7/e/7e2776f8ddd1c7941971c9f23df8e529bce0986b.png)

---

<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:** [8 May 2022 15:32 UTC](https://discourse.nodered.org/t/converting-an-array-of-bytes-into-a-int16-to-write-in-a-modbus-server-holding-register/62370/12 "2022-05-08T15:32:08Z")

</div>

How do you expect to make 16 integers from 2 values?

Please explain exactly what you expect the output to be?

---

<div class="post-metadata">

**Author:** ![Theodros](https://sea2.discourse-cdn.com/flex026/user_avatar/discourse.nodered.org/theodros/32/61068_2.png) [@Theodros](https://discourse.nodered.org/u/Theodros)\
**Post date:** [8 May 2022 15:33 UTC](https://discourse.nodered.org/t/converting-an-array-of-bytes-into-a-int16-to-write-in-a-modbus-server-holding-register/62370/13 "2022-05-08T15:33:59Z")

</div>

I actually have 16, I'm making a drawing. It might be easier to understand

---

<div class="post-metadata">

**Author:** ![Theodros](https://sea2.discourse-cdn.com/flex026/user_avatar/discourse.nodered.org/theodros/32/61068_2.png) [@Theodros](https://discourse.nodered.org/u/Theodros)\
**Post date:** [8 May 2022 15:42 UTC](https://discourse.nodered.org/t/converting-an-array-of-bytes-into-a-int16-to-write-in-a-modbus-server-holding-register/62370/14 "2022-05-08T15:42:23Z")

</div>

First the person will select the value It wants (B1 = 1 or 0) and wich variable it want's to change (S1 going from 0 to 79) :

![image](https://us1.discourse-cdn.com/flex026/uploads/nodered/original/3X/1/1/111c38e74f199c985366662e54fbdeacf80d7506.png)

When validated,  
 ![image](https://us1.discourse-cdn.com/flex026/uploads/nodered/original/3X/0/5/0519ab325b990e15a8df4a85cc2f0484080e0675.png)

I'm putting the value of B1 in an array at the adress S1:  
 ![image](https://us1.discourse-cdn.com/flex026/uploads/nodered/original/3X/6/6/66969ede372d760f236f772c5a7d94d5852c5e3a.png)

The last and missing part is the conversion.

And If you ask why a table of 79, It is because there's 79 variables that can be selected and modified.

---

<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:** [8 May 2022 15:46 UTC](https://discourse.nodered.org/t/converting-an-array-of-bytes-into-a-int16-to-write-in-a-modbus-server-holding-register/62370/15 "2022-05-08T15:46:27Z")

</div>

ok, so how do you write to modbus - all 79 values at once? or upon value change + button press?

I dont understand where 16 comes into this?

---

<div class="post-metadata">

**Author:** ![Theodros](https://sea2.discourse-cdn.com/flex026/user_avatar/discourse.nodered.org/theodros/32/61068_2.png) [@Theodros](https://discourse.nodered.org/u/Theodros)\
**Post date:** [8 May 2022 15:49 UTC](https://discourse.nodered.org/t/converting-an-array-of-bytes-into-a-int16-to-write-in-a-modbus-server-holding-register/62370/16 "2022-05-08T15:49:40Z")

</div>

Depending on wich variable the person choose (line 15-17 on the last code pic) I will return a table of 16 that will be converted to UINT16be and after a button press will be sent to write to the holding register of a modbus server.

---

<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:** [8 May 2022 15:56 UTC](https://discourse.nodered.org/t/converting-an-array-of-bytes-into-a-int16-to-write-in-a-modbus-server-holding-register/62370/17 "2022-05-08T15:56:55Z")

</div>

I am slowly extracting the necessary info from you and trying to peice this together.

correct me if any of this is wrong...

- User selects a parameter
- User sets a TRUE or FALSE (1 or 0)
- User "stores this" setting in flow memory
- Once user has entered all 16 values, you want to create a 1 WORD (16 bit) value from the 16 "bits" entered - then you write this to ModBus?

---

<div class="post-metadata">

**Author:** ![Theodros](https://sea2.discourse-cdn.com/flex026/user_avatar/discourse.nodered.org/theodros/32/61068_2.png) [@Theodros](https://discourse.nodered.org/u/Theodros)\
**Post date:** [8 May 2022 15:58 UTC](https://discourse.nodered.org/t/converting-an-array-of-bytes-into-a-int16-to-write-in-a-modbus-server-holding-register/62370/18 "2022-05-08T15:58:55Z")

</div>

No problem It's hard to understand when you're not the one coding.

He just enter one value but that's exactly It 👍

---

<div class="post-metadata">

**Author:** ![Theodros](https://sea2.discourse-cdn.com/flex026/user_avatar/discourse.nodered.org/theodros/32/61068_2.png) [@Theodros](https://discourse.nodered.org/u/Theodros)\
**Post date:** [8 May 2022 16:00 UTC](https://discourse.nodered.org/t/converting-an-array-of-bytes-into-a-int16-to-write-in-a-modbus-server-holding-register/62370/19 "2022-05-08T16:00:06Z")

</div>

Thank you for taking your time with my problem

---

<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:** [8 May 2022 16:02 UTC](https://discourse.nodered.org/t/converting-an-array-of-bytes-into-a-int16-to-write-in-a-modbus-server-holding-register/62370/20 "2022-05-08T16:02:21Z")

</div>

ok, nearly there.

If the user enters 1 for address 0 then that would make `{"S1":0,"B1":1}` right?

So what value do you want to write to ModBus? Why are you looping 16 times?

What might make it easier to see the bigger picture by providing a few examples.

e.g.

- user selects address 2 & enters 0, I would get `{"S1":2,"B1":0}` and would expect to write xxxx to ModBus at address yyyy?
- user selects address 15 & enters 1, I would get `{"S1":15,"B1":1}` and would expect to write xxxx to ModBus at address yyyy?

[Next page](https://discourse.nodered.org/t/converting-an-array-of-bytes-into-a-int16-to-write-in-a-modbus-server-holding-register/62370.md?page=2)