CRC error when talking to WEG Drive

I am using the mod bus library to talk to a WEG drive. For the WEG drive it has an additional function:

    Function 43 – Read Device Identification

An example usage looks like:

.::Request::.

Slave Address Function MEI Type Reading Code Object Number CRC low CRC High

[01][2B][0E][01][00][70][77]

.::Response::.

Slave Address Function MEI Type Reading Code Confirmity Level More Follows Next Object Number of Objects Object Code Object Size Object Value ... CRC low CRC High

[01][2B][0E][01][81][00][02][01][1B][Hex of 'CFW-11 220 - 230 V 10A /8A'][02][05][Hex of 'V4.50'][B2][8F]

So to send this request I am using the following code (just experimental code, nothing special):

    uint8_t raw_req[] = { 0x01, 0x2B, 0x0E, 0x01, 0x00 };
    int rc = 0;
    uint8_t rsp[MODBUS_RTU_MAX_ADU_LENGTH];

    rc = modbus_send_raw_request(m_modbus, raw_req, 5 * sizeof(uint8_t));
    if (rc == -1 || rc < 5)
    {
        std::cout << "Raw didn't work " << rc << std::endl;
        return;
    }
    rc = modbus_receive_confirmation(m_modbus, rsp);

    if (rc == 0)
    {
        std::cout << "Ignored" << std::endl;
    }
    else if (rc == -1)
    {
        fprintf(stderr, "ID: %s\n", modbus_strerror(errno));
        return;
    }
    else
    {
        for (unsigned int i=0; i < rc; i++) {
            printf("%.2X ", rsp[i]);
        }
    }

With modbus debug mode enabled I am seeing the following output:

    [01][2B][0E][01][00][70][77]
    Waiting for a confirmation...
    01><2B><0E><01><81>
    ERROR CRC received 181 != CRC calculated BF34
    ID: Invalid CRC

It looks like maybe the WEG drive is not writting the full response, or modbus isn't properly reading it? The <01><81> should be 'Reading Code' and 'Conformity Level', but modbus library thinks it is the CRC because it is at the end of the response.

stephane / libmodbus

CRC error when talking to WEG Drive #114