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Some pins stuck at odd values

Jon Gelderloos
Prodigy 20 points
Other Parts Discussed in Thread: MSP430G2452

Im working on a project on my msp430g2452 device and I am using P1.0, 1.3, 1.4, 1.5, 1.6, and 1.7 for adc10. I have all the ports configured fine but P1.7 is stuck at 3.4V and P1.5, 1.4, and 1.3 are all around 2V. All the other pins i want to use for adc10 are fine. I have even tried a new very basic project to turn the ports on and off and they are still stuck. Is something wrong with my device?

  • 0
    Guru 58965 points

    Someone (not you) may have made a mistake and drives the TEST pin high. As a result, P1.7, P1.6, P1.5 and P1.4 cannot be controlled by user code. .

    If you pull out the J3 TEST jumper, those pins will work fine. However, the debugger will not work without that jumper in place.

    Alternatively, you could unplug LaunchPad from the USB port and plug it back a few seconds later, TEST pin will not be high anymore. However, after you use the debugger, TEST pin will be driven high again.

    The "debugger" is the one that causes this bug!

  • 0 in reply to old_cow_yellow
    Guru 227245 points

    It's actually a design flaw.

    For SBW (which is necessary for debugging), the TEST pin is required. However, the same pin will switch the 4-pin JTAG pins on and off, probably even during SBW access. Pulling SBWTCK low after an SBW action will likely disturb the future SBW communication while keeping it high will render the pins P1.4..P1.7 virtually useless. Even if the debugger can cope with pulling SBWTCK low after any SBW action, during this action those pis will likely exhibit erraneous behavior.

    Not a good idea to pick pins for JTAG which have multiple use and cannot be replaced by others (as the plain GPIO pins P2.0..P2.5 could)

  • 0 in reply to old_cow_yellow
    Prodigy 20 points

    Well i tired removing the test pin from J3 and I am still seeing the same thing. Ive also tried unplugging it and reloading with no results. Luckily I just got the capacitive touch booster pack today and it has the same device that I am using. I loaded up my code and all the pins that I am sampling on are near ground where they should be. Looks like something I did must have shorted something in my old chip to cause that problem.

  • 0 in reply to Jon Gelderloos
    Guru 227245 points

    Jon Gelderloos said:
    Looks like something I did must have shorted something in my old chip to cause that problem.

    There is one scenario where this could happen: if you power the MSP from an external source (not the FET) but do not apply the external VCC. If you then apply a voltage to any port pin, current flows from that pin to VCC, eventually powering the device. However, if htis current permanently exceeds 2mA, it might melt the clamp diodes, making a permanent connection to VCC (or breaking up the connection, both can happen). And over this bridge, otehr pins belonging to the JTAG logic might be affected too. It is, however, less likely than the TEST pin problem, but if you excluded this, and a replacement chip works...

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