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MSP430AFE253 UART Stops Functioning

MAC Engineering
Expert 1460 points
Other Parts Discussed in Thread: MSP430AFE253

I am not sure if the UART is extremely sensitive to ESD, or there could be a batch of uC that the UART is not functioning correct?

When performing a rework of a circuit (Use Ohm meter for checking connections, thus current), the UART quit functioning with the replacement MSP430AFE253.

I have had 3 AFE253 devices where the UART would not function, when replacing the device with AFE252, the UART started working again.

In all cases above where the UART does not work, I am sending a signal to the uC which calls the UART ISR.  By placing a break point within the ISR, and checking that the signal entering the uC is valid, the ISR break point is never hit.  Thus, the signal is never triggering the ISR call for transmission.

Has any one else had this problem?  Or, is there a known problem with the UART in the MSP430AFE253

  • 0
    Guru 227245 points

    MAC Engineering said:
    is there a known problem with the UART in the MSP430AFE253

    The only known problem (you can check this by reading the errata sheet, which you should have downlaoded alogn with the data sheet and the users guide) is with two stopbits, where a missing second stop bit isn't reported by a framing error.

    The only difference between the 252 and the 253 is the additional optional SD24A stream output on the pin that is also used for UART RX. But if you poroperly configure the port, this shouldn't make a difference.

    However, not getting an interrupt may have several reasons, including a wrong baudrate. If you don't use an external crystal for the reference clock, the tolerance of the internal DCO may cause significant differences in timing. The differences may be even larger for different batches of devices.

  • 0 in reply to Jens-Michael Gross
    Expert 1460 points

    Nope, the code works on one and not the other uC.

    Yep, nothing in the errata.

    TI application engineer has stated that the DCO works fine for my baud rate.

    Problem is either in the IC or my methods of soldering it.  I am using ESD protection. 

  • 0 in reply to MAC Engineering
    Guru 227245 points

    The MSP also has some ESD protection by its clamp diodes. Over/undervoltage on any input pin (including the UART pins, as the frontend is the same GPIO driver/input circuitry) is routed to VCC/GND by two diodes that can sink/source 2mA rated current. However, ultrashort transients may come through and damage the prot pin. But then, there is no difference between the two processor types, so I guess it's just coincidence that oen works whiel the other fails.

    But what if the signal voltages are above VCC? It may work for some time and then the clamp diodes fail and the port is damaged. Also, what is the sensing voltage/current of your Ohmmeter? If doing a measurement on unpowered MSP, a sensing current of above 2mA can damage the clamp diodes.

  • 0 in reply to Jens-Michael Gross
    Expert 1460 points

    I was hoping to see if a TI rep would respond, or if others have the same problem,? I want to be confident for a production run/take appropriate measures for any introduced error on my behalf.

    Fluke 189, Ohms mode I = 1mA

    I have read the datasheet, but thank you for your suggestions in case I may have missed something.

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