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TEST pin pull down resistor on 'A' and non-'A' version

Andre40757
Prodigy 40 points
Other Parts Discussed in Thread: MSP430F1121A, MSP430F1121

Hi there,

Can you confirm if there is a pull down resistor on the TEST pin of MSP430F1121A?  Our test setup indicates to us that the 'A' version of the F1121 does not have this pull down resistor on it compared to our earlier use of the non-'A' version.

The datasheet shows this TEST pin should be between 25-90Kohms and also states that this pull down is present in "all versions".

We have a 30Kohm resistor pulldown externally on this pin and currently our test station measures this pin as 30Kohms whcih shows no resistance in parallel to this external pull down resistor.  When we used the non-A version of this device, the test station measured about 18Kohm (30Kohm external in parallel with ~40Kohm).

Please confirm this as we need to better understand if this is correct or not.

  • 0
    Guru 227245 points

    IIRC, the test pin is current driven. The default state is leaving it floating. There is no internal pull-down resistor, only the semiconduction circuitry that acts as a lowad if the input voltage exceeds a certain threashold and causes an input current that will at some point trigger the TEST pin function. The threshold voltage may vary and maybe the test voltage of your test equipment isn't high enough for this MSP and therefore only your external resistive load is detected.

    But that's really old information I'm digging out of my memory. And maybe I'm wrong or this info is outdated. It dates back to 1x family.

  • 0 in reply to Jens-Michael Gross
    Guru 92251 points

    Datasheet SLAS241I covers the MSP430F1121 'A' and non-'A' versions. There is the following note 2, which indicates the TEST pull down resistor is present on both 'A' and non-'A' versions:

    The Port P1, P1.4 to P1.7, input/output with Schmitt trigger and in-system access features section of the datasheet also shows a 60k typical pulldown on the test pin on all versions.

  • 0 in reply to Chester Gillon
    Guru 227245 points

    You're right, the schematics and data tables on these devices indeed show a pulldown resistor.
    The description of the TEST pin in the unused pins table lists a 30k pulldown resistor for 11x1 devices and open for the 11x1a, 11x2, 12x and 12x2 devices. This table hasn't been updated for 14x and 16x devices at all. At least not until revision f of the users guide, which is the latest atm.

    The TEST pin is also used to blow the JTAG fuse, by forcing 100mA into it (requires 6-7V) for 1 ms.

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