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Problem withTEST/SBWTCK pin in MSP430F5340

Daniel Vazquez1
Prodigy 60 points
Other Parts Discussed in Thread: MSP430F5340, MSP430F5528, MSP430F6731

Hi all,

I am using the MSP430F5340 in a project. the programing of MSP430 is done through the Spy-bi-wire connection. I have routed the pins RST/NMI/SBWTDIO (pin 46) and TEST/SBWTCK (pin 41), GND and 3.3V to a connector (same that figure 2-3 in MSP430 Hardware Tools User's Guide, Pag 24). The microcontroller is properly programmed. I have the next problem:

When the microcontroller is running, if I touch the pin TEST/SBWTCK in connector, the microcontroller is reset. the connection between the connector's pin and the MSP430's pin is through a 0 Ohm resistor. I need to know if we could to solve this problem with a soft modification, since we have fabricated and assembly the PCBs. This could be a problem in ESD testing or a involuntary reset of the system. Thank.

Best regards,

Daniel.

  • 0
    TI__Guru 56650 points

    Daniel,

    according to some experience, what could happen is that the noise at TEST pin will make the device entering debug mode (you can refer to the SLAU320 for this). This is also usually caused by poor PCB layout with regard to noise, and also it is important to notice that the JTAG pinout should be located as close as possible with the device pins to reduce the noise susceptibility.

    Could you also try to add an external 4.7KOhm pull-down resistor at the TEST pin to see whether this helps.

  • 0 in reply to Leo Hendrawan
    Intellectual 565 points

    Hi,

    in a MSP430F5528 design I also had an electromagnetic issue with the TEST/SBWTCK pin.  I have a 15 mm long track between the floating pin and my 2-wire JTAG connector. Always when I approached a shielding cover the MSP430 performed a flash memory access violation interrupt (ACCVIFG). This was caused by the clock of a DC/DC converter in another corner of the PCB which appeared as 500 mV ripple on the TEST/SBWTCK line. A 4.7 kOhm pull-down resistor to ground as suggested above did not help. A  pull-up resistor to DVCC solved the problem in my case. JTAG seems to work with it.

  • 0 in reply to Jan Burgemeister
    Guru 227245 points

    Jan Burgemeister said:
    A 4.7 kOhm pull-down resistor to ground as suggested above did not help. A  pull-up resistor to DVCC solved the problem in my case.

    Strange that pullup works while pulldown won't. But you're not the only one observing this.

    Jan Burgemeister said:
    JTAG seems to work with it.

    Sure, the JTAG signal is driven by lower impedance than 4.7k. However, the latest FET430UIF have 1k series resistors on the signal lines. This results in a limited signal swing.
    Also, this keeps the JTAG circuitry active all the time, increasing power consumption.

  • 0 in reply to Leo Hendrawan
    Intellectual 485 points

    Sir,

    We faced a similar problem where in MSP430 was in inadvertently getting into debug mode and the watch dog reset pulse does not RESET the micro controller.

    Only a power down &up CYCLE RESTORES the operation.

    Is not RESET is supposed to be a non mask able control on the microcontroller  paving way for an un interruptalble  operation of the controlling device with the help of an external watch dog timer.

    Is there no other method by which the processor can be woken up .

    Regards

    VTC

  • 0 in reply to Vijeth K Shastry
    Guru 227245 points

    Vijeth K Shastry said:
    Is not RESET is supposed to be a non mask able control

    The RESET signal to the CPU is not maskable. However, the port pin logic for the RST pin can be configured to something else. Like NMI. Or SBW.

  • 0 in reply to Leo Hendrawan
    TI__Expert 3311 points

    Hello Champs,

    It's pretty long time from posting this issue, but one of my customer who use MSP430F6731 also have similar issue.

    One question : 

    To add 4.7kOhm pull-down resister at the TEST pin is applicable for both 4-wire and 2-wire(SBW) JTAG connection?

    Thanks.

    Ernest

  • 0 in reply to Ernest Cho
    Guru 227245 points
    Adding a resistor isn't a problem for SBW, as long as there is no capacitance. The driving strength of the FET and/or the MSP is high enough to drive against a pure resistive pull-down without disturbing the SBW signals.

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