modbus_reply_exception

Name

modbus_reply_exception - send an exception response

Synopsis
    int modbus_reply_exception(modbus_t *ctx, const uint8_t *req, unsigned int exception_code);

Description

The modbus_reply_exception() function shall send an exception response based on the 'exception_code' in argument.

The libmodbus provides the following exception codes:

    •   MODBUS_EXCEPTION_ILLEGAL_FUNCTION (1)

    •   MODBUS_EXCEPTION_ILLEGAL_DATA_ADDRESS (2)

    •   MODBUS_EXCEPTION_ILLEGAL_DATA_VALUE (3)

    •   MODBUS_EXCEPTION_SLAVE_OR_SERVER_FAILURE (4)

    •   MODBUS_EXCEPTION_ACKNOWLEDGE (5)

    •   MODBUS_EXCEPTION_SLAVE_OR_SERVER_BUSY (6)

    •   MODBUS_EXCEPTION_NEGATIVE_ACKNOWLEDGE (7)

    •   MODBUS_EXCEPTION_MEMORY_PARITY (8)

    •   MODBUS_EXCEPTION_NOT_DEFINED (9)

    •   MODBUS_EXCEPTION_GATEWAY_PATH (10)

    •   MODBUS_EXCEPTION_GATEWAY_TARGET (11)

The initial request req is required to build a valid response.

Return value

The function shall return the length of the response sent if successful. Otherwise it shall return -1 and set errno.

Errors

    •   EINVAL, the exception code is invalid

See also

    •   modbus_reply ⟨modbus_reply.md⟩