2016-05-26, 08:54 PM
I think RXD and TXD must be crossed (RXD pin 8 and TXD pin 10). I don't think that the HMC5883L standalone (no gyro and no accelerator) is supported by OP.
If SDA and SCL are only for HMC5883L you don't need to connect them for OP.
If SDA and SCL are only for HMC5883L you don't need to connect them for OP.