Debugging guide for serial interfaces

The aim of this chapter is to give some pointers on what to check if some issues are seen when using the UART, SPI, or I2C interfaces.

Note: TI only supports how to use the serial interface modules and the TI supplied drivers for these interfaces. TI are not able to help on the usage of a non-TI device connected to I2C, SPI or UART.

I2C

  • The I2C interface needs an external pull-up resistor. On the LauchPad these are 3.3 kOhm.

  • Measure the waveform on the I2C interface with an oscilloscope to verify the SCL and SDA levels

  • Monitor the interface with a logic analyzer. Check that data on the bus is the same as the wanted data.

  • Check the interface by reading out the device ID of the sensor.

  • Check the slave address. The I2C module uses a 7-bit address. The last 8th bit is the data direction bit. This last bit is appended automatically by the driver/HW. The Slave address given to the driver has therefore to be 7-bit.

  • Ensure that the readCount and writeCount is according to the register size used. If the result register in the sensor is 16-bit, the readCount has to be set to 2.

SPI

  • Monitor the interface with a logic analyzer. Compare the waveform with the waveform given in the datasheet for the device you are communicating with.

  • Check that the CSn is set correctly.

  • Check that the frame format is set correctly. Check if the device you are communicating with uses SPO = 1 or 0 and SPH = 1 or 0.

UART

  • Make sure to connect the TX pin of one device to the RX pin of the other device, and vice versa. If flow control is enabled, then the same applies towards the CTS and RTS pins.

  • Verify all communication settings between devices, including baud rate, data length, stop/parity bits and flow control.

  • Evaluate the interface with a logic analyzer or oscilloscope, using an analyzer tool if possible to convert the waveforms into their numerical counterpart.