Data length error, expected x got y (x > y)

Industrial
1

We can communicate with a device at /dev/ttyAMA0.

It uses ModBus RTU, 9600 baud rate.

But when I try to read data according to the documentation of the device I am getting the error:

"Data length error, expected 7 got 2"

The reading configuration:

{
    'fc': 3, // Modbus function 0x03
    'unitid': 0,

    'address': 2,
    'quantity': 1
}

We also get a timeout error quite often. So there might be problems regarding parity and stop bits, but I cannot see, how we configure this in node-red-contrib-modbus.

Any idea for the reason of this kind of problem?

2

Can you send part of the flow? Tell me what device it is.
I think I once had a case where the device responded to an even number in quantity.

3

I've figured how to set parity and the number of data bits etc

This can be done by selecting Serial Expert for the modbus server.

I think the problem could also be caused by missed termination in the RS485 network, because no matter what I am trying with baud rate, parity, data bits etc., I am getting errors only (data length error or timeout). So we will check the hardware configuration there, too.

Here is the flow, but

[
    {
        "id": "1d730243db9feb8a",
        "type": "tab",
        "label": "ModBus Seriell ClampOn ",
        "disabled": false,
        "info": "",
        "env": []
    },
    {
        "id": "a4c9a2f40bc6910c",
        "type": "modbus-flex-getter",
        "z": "1d730243db9feb8a",
        "name": "Serial ModBus ClampOn",
        "showStatusActivities": true,
        "showErrors": true,
        "showWarnings": false,
        "logIOActivities": false,
        "server": "9918af96579ce096",
        "useIOFile": false,
        "ioFile": "",
        "useIOForPayload": false,
        "emptyMsgOnFail": false,
        "keepMsgProperties": true,
        "delayOnStart": false,
        "enableDeformedMessages": false,
        "startDelayTime": "2",
        "x": 570,
        "y": 180,
        "wires": [
            [
                "1e69851eced5d421"
            ],
            [
                "699db3ec86531f6b"
            ]
        ]
    },
    {
        "id": "7bb0e6a2935402b5",
        "type": "inject",
        "z": "1d730243db9feb8a",
        "name": "trigger",
        "props": [
            {
                "p": "payload"
            },
            {
                "p": "topic",
                "vt": "str"
            }
        ],
        "repeat": "",
        "crontab": "",
        "once": false,
        "onceDelay": 0.1,
        "topic": "",
        "payload": "true",
        "payloadType": "bool",
        "x": 110,
        "y": 100,
        "wires": [
            [
                "cdacefc17ac2b270"
            ]
        ]
    },
    {
        "id": "cdacefc17ac2b270",
        "type": "function",
        "z": "1d730243db9feb8a",
        "name": "FC ??? -- 4 517 [6]",
        "func": "\nmsg.payload = { \n    // value is true WHY ????\n    // value: msg.payload,\n    // https://blog.softwaretoolbox.com/opc-modbus-function-codes\n    'fc': 3,\n    'unitid': 0,\n\n    'address': 1,\n    'quantity': 1\n};\nreturn msg;",
        "outputs": 1,
        "timeout": "",
        "noerr": 0,
        "initialize": "",
        "finalize": "",
        "libs": [],
        "x": 330,
        "y": 180,
        "wires": [
            [
                "a4c9a2f40bc6910c"
            ]
        ]
    },
    {
        "id": "1e69851eced5d421",
        "type": "debug",
        "z": "1d730243db9feb8a",
        "name": "debug 4",
        "active": true,
        "tosidebar": true,
        "console": false,
        "tostatus": false,
        "complete": "false",
        "statusVal": "",
        "statusType": "auto",
        "x": 820,
        "y": 140,
        "wires": []
    },
    {
        "id": "699db3ec86531f6b",
        "type": "debug",
        "z": "1d730243db9feb8a",
        "name": "debug 7",
        "active": true,
        "tosidebar": true,
        "console": false,
        "tostatus": false,
        "complete": "false",
        "statusVal": "",
        "statusType": "auto",
        "x": 820,
        "y": 220,
        "wires": []
    },
    {
        "id": "9918af96579ce096",
        "type": "modbus-client",
        "name": "",
        "clienttype": "serial",
        "bufferCommands": true,
        "stateLogEnabled": true,
        "queueLogEnabled": false,
        "failureLogEnabled": true,
        "tcpHost": "127.0.0.1",
        "tcpPort": 502,
        "tcpType": "DEFAULT",
        "serialPort": "/dev/ttyAMA0",
        "serialType": "RTU",
        "serialBaudrate": "9600",
        "serialDatabits": "5",
        "serialStopbits": 1,
        "serialParity": "none",
        "serialConnectionDelay": 100,
        "serialAsciiResponseStartDelimiter": "0x3A",
        "unit_id": 0,
        "commandDelay": 0,
        "clientTimeout": 2000,
        "reconnectOnTimeout": false,
        "reconnectTimeout": 2000,
        "parallelUnitIdsAllowed": false,
        "showErrors": true,
        "showWarnings": true,
        "showLogs": true
    },
    {
        "id": "2d201daaac4afbbb",
        "type": "global-config",
        "env": [],
        "modules": {
            "node-red-contrib-modbus": "5.44.1"
        }
    }
]

But I cannot change the value for this configuration field: "serialAsciiResponseStartDelimiter": "0x3A", right?