bug, readHoldingRegisters cannot read over 128

[pmingkr]

      const { response } = await client.readHoldingRegisters(
        0,
        129
      );
      console.assert(response.body.valuesAsArray.length === 1);

[stefanpoeter]

That is not very much you are giving me here.

[pmingkr]

I made sample code for it. but I met a different error message. https://codesandbox.io/p/sandbox/hardcore-chihiro-sclvqt?file=%2Findex.js%3A10%2C4

[stefanpoeter]

The "ERR_OUT_OF_RANGE" probably occurs because you did not provider a buffer for the modbus registers.

[pmingkr]

The "ERR_OUT_OF_RANGE" probably occurs because you did not provider a buffer for the modbus registers.

No it's not. RangeError [ERR_OUT_OF_RANGE]: The value of "value" is out of range. It must be >= 0 and <= 255. Received 258 It happened because it tried to access index 258, but I had requested indices from 0 to 128.

[stefanpoeter]

I see. The modbus specification allows a total quantity of 125 registers to be fetched with one request. The Error Message comes from the array or buffer that cannot fit more that 255 bytes in there. The error message is a bit cryptic I admit.

[pmingkr]

I see. The modbus specification allows a total quantity of 125 registers to be fetched with one request. The Error Message comes from the array or buffer that cannot fit more that 255 bytes in there. The error message is a bit cryptic I admit.

Could you tell me the source of it? I checked the Modbus Organization's document, but I could not find it. https://www.modbus.org/docs/Modbus_Messaging_Implementation_Guide_V1_0b.pdf

[stefanpoeter]

You find the PDF here: https://modbus.org/docs/Modbus_Application_Protocol_V1_1b.pdf

[pmingkr]

You find the PDF here: https://modbus.org/docs/Modbus_Application_Protocol_V1_1b.pdf

Thanks for your explanation.

jsmodbus can read 127 registers. it seems it's a also broken behavior.

[stefanpoeter]

you are right @pmingkr There should be a error when issuing a request that reads more than 127 register. I am always happy for contributions :-)