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MSP-FET: 3.3V on RST line after power up causes problems?

Alex Kucherov
Prodigy 220 points
Part Number: MSP-FET
Other Parts Discussed in Thread: UNIFLASH,

Hello, 

I'm using the MSP-FET, together with the MSP-FET-432ADPTR , to program an MSP432P401R in a production line through UNIFLASH.

In my setup the MSP432 is not powered when first connected to the programming station. The operator has to press a button to turn on the voltages. 

However, when connected to the MSP-FET, voltages appear on the MSP432 voltage rail even without turning on the power and causes an unexpected behavior. 

The switch setting on the MSP-FET-432ADPTR is set to "sense", and "VCC tool" is not connected anywhere on my board. Somehow, the MSP-FET is powering the MSP432.

I think this is caused by the "RST" line which, according to the datasheet and to measurements, is being actively driven to +3.3V on power up and through internal protection diodes powers the device. 

Is this indeed the case? Is there any way to change this power up configuration of the RST line?  

  • 0
    TI__Guru**** 317180 points

    Reading http://www.ti.com/lit/ug/slau647m/slau647m.pdf it looks like the RST pin from the MSP-FET is set to pull-up when powering up the MSP-FET. Since having one pin at 3.3 V when all the other pins are at 0 V (which will be the case before powering up the DUT) the absolute maximum ratings for the chip is not followed  and you will get forward biased ESD diodes. 

    It sounds like you need to ensure that the DUT is in active reset when you power it up. Not sure what would be the best way to do this, if switching in the reset signal could be an option.

    On a side note, have you looked into http://www.ti.com/tool/MSP-GANG which I believe is a tool that is targeting mass production. The MSP-FET is a typical debug tool. 

  • 0
    Guru 33653 points

    Alex Kucherov said:

    I think this is caused by the "RST" line which, according to the datasheet and to measurements, is being actively driven to +3.3V on power up and through internal protection diodes powers the device. 

    MSP432 are ARM devices, where SWD interface with dedicated DATA / CLK line is used. If  RESET line is source of your problem, don't use it. It should work fine without it.

  • 0 in reply to zrno soli
    Prodigy 220 points

    zrno soli said:
    MSP432 are ARM devices, where SWD interface with dedicated DATA / CLK line is used. If  RESET line is source of your problem, don't use it. It should work fine without it.

    Disconnecting the RESET line doesn't seem to work, UniFLASH reports a communication error with the device. 

  • 0 in reply to Alex Kucherov
    TI__Guru**** 317180 points

    Not sure how the MSP-FET operate together with MSP432 but in many cases the reset line has to be toggled to initiate connection. Also when you disconnected this line, did you leave the reset line be undefined at the MSP432 side? 

  • 0 in reply to TER
    Prodigy 220 points

    No, the reset line on the MSP432 side is pulled up with 100K resistor.

    I've just examined the voltages again, and the MSP-FET is driving 3.3V on the RST/SWDIO/SWCLK lines even when no target device is connected and no voltage is present on the sense pin. So, its probably not just the RST line but also the other two SWD lines which are causing the issue. 

    Can the MSP-FET level shifter be configured to pull these lines to '0' while no voltage is present on sense pin? 

  • 0 in reply to Alex Kucherov
    Guru 33653 points

    Alex Kucherov said:

    No, the reset line on the MSP432 side is pulled up with 100K resistor.

    I've just examined the voltages again, and the MSP-FET is driving 3.3V on the RST/SWDIO/SWCLK lines even when no target device is connected and no voltage is present on the sense pin. So, its probably not just the RST line but also the other two SWD lines which are causing the issue. 

    Can the MSP-FET level shifter be configured to pull these lines to '0' while no voltage is present on sense pin? 

    SWD lines when target device is not under master control should be pulled (internally) by target device itself (or external resistors on target device board). In this state master device lines should be configured as floating input (Hi-Z). Don't know about MSP-FET line states.

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