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P2 Eval Board Owners, I need your help! — Parallax Forums

P2 Eval Board Owners, I need your help!

P2 Eval Board Owners, I need your help!

Could you please unplug the USB cable and remove all the jumpers on your P2 Eval board that surround the P2 chip? Also, remove all accessory boards from the 2x6 headers. Then, could you please measure the resistances between each Vxxxx pin and GND?

The Vxxxx pins are the 2nd and 5th pins on each 1x6 male header that surrounds the P2. It doesn't matter which side you count from. They are the V's in this pattern: IVIIVI

I would think the negative meter probe would go to GND (any of those four GND posts) and the positive meter probe would go to the Vxxxx pin header pin being measured. You'll need to measure with the VIO pin being subjected to the positive voltage. Otherwise, you may wind up measuring the clamp diode to GND, which we don't care about.

If you could report your measurements as such, it would be most helpful:

V0007 = ? ohms
V0815 = ? ohms
V1623 = ? ohms
V2431 = ? ohms
V3239 = ? ohms
V4047 = ? ohms
V4855 = ? ohms
V5663 = ? ohms

We have some trouble with the new silicon, where some VIO pins are shorted to GND (5..20 ohms), somewhat randomly. I am really wondering if the old silicon exhibits these characteristics, at all.



  • jmgjmg Posts: 14,820
    ...and maybe also measure the lateral injection current that flows out of V2431 ?
    On my Eval, with all VIO jumpers removed, and VDD powered, I measure that ~10mA can flow out of V2431, (V2431 to mA meter to GND)
  • I looked at 3 of the 8 pins. They move around a bit, but was getting readings of 60 to 80k ohm when settled. However I'll repeat later tonight.
  • cgraceycgracey Posts: 13,627
    Yeah, there's almost 10uF of bypass on each VIO. It will take a few seconds to settle during the measurement.
  • I repeated the same measurements on the same pins using Fluke 75 dvm, its saying 3 to 7 Megohms.

    The fluke measures with an open circuit voltage around 0.74v, whereas the above was with a benchtop dmm which uses around 2.6v. That might explain the difference.

  • cgraceycgracey Posts: 13,627
    Tubular wrote: »
    I repeated the same measurements on the same pins using Fluke 75 dvm, its saying 3 to 7 Megohms.

    The fluke measures with an open circuit voltage around 0.74v, whereas the above was with a benchtop dmm which uses around 2.6v. That might explain the difference.

    That's good. Thanks for checking those. I'm wondering if we'll see anything really low-impedance out there.
  • roglohrogloh Posts: 3,632
    edited 2019-08-15 09:21
    Chip, I happened to bring my P2-EVAL on vacation in case of rainy days and found my board must have over 2Mohm of impedance on all 8 Vxxx pins when I tested it, it keeps climbing above my multimeter's limit as it charges up. Using its 20Mohm scale shows open circuit on all pins for some reason (probably just my crappy meter I brought along), and on the 2Mohm scale it just slowly rises over several seconds until it goes above 2Mohm. So no low impedances on this one.
  • Mine seem to behave oddly. They mostly measure in the 4Mohm range but occasionally one will measure less than 1Mohm. I saw one measure as low as 60Kohm at first but when I tried it again it was in the 4Mohm range. Now they all measure in the 4Mohm range. Also, their resistance seems to keep increasing the longer I hold the meter probe to the pin. I'm using a Fluke 115.
  • evanhevanh Posts: 11,845
    500 uA constant current source diode test:

    V0007 = >4.0 volts
    V0815 = 2.50 volts
    V1623 = 2.34 volts
    V2431 = 1.84 volts
    V3239 = 2.42 volts
    V4047 = 2.57 volts
    V4855 = 1.62 volts
    V5663 = >4.0 volts
  • I'm on vacation right now, and very sad I can't contribute. I can do my measurements only in September.

    Kind regards, Samuel Lourenço
  • evanhevanh Posts: 11,845
    David Betz wrote: »
    Also, their resistance seems to keep increasing the longer I hold the meter probe to the pin. I'm using a Fluke 115.
    Expected behaviour because of the capacitors.

  • cgraceycgracey Posts: 13,627
    Thanks, Guys, for trying this. No problems found, so far.

    We could still use more data, if anyone reading this has a P2 Eval and hasn't taken these measurements, yet.

  • I see the following (measuring from GND on one of the expansion headers and with a 15 year old cheap Japanese DMM):
    All Vabcd pins go almost immediately to very high impedance except V1623 which stays around 7M ohm
  • V0007 = >20 M Ohm
    V0815 = >20 M Ohm
    V1623 = >20 M Ohm
    V2431 = >20 M Ohm
    V3239 = >20 M Ohm
    V4047 = >20 M Ohm
    V4855 = >20 M Ohm
    V5663 = >20 M Ohm

    Measurements taken with a TENMA 72-050 ('1988 "improved series". At the time, the ohmic scale being able to reach up to 20 MOhm was one of the upgrades, when compared to the first lots of that series ('1987)).

    Old, for sure, but faithful as Yellowstone's geyser.
  • All 8 pins reading 4-6 Megohms here.
  • V0007 = 16M ohms
    V0815 = 10M ohms
    V1623 = 15M ohms
    V2431 = 9M ohms
    V3239 = 10M ohms
    V4047 = 8M ohms
    V4855 = 9M ohms
    V5663 = 9M ohms
  • DavidZemonDavidZemon Posts: 2,937
    edited 2019-08-15 13:48
    All of mine settle between 8M and 10M ohms
  • cgraceycgracey Posts: 13,627
    Thanks, Guys!

    Who else?
  • Fluke 87 meter, about 100 mV sense voltage,
    final settled values when .01M digit held for at least 5 sec:

    V0007 = 5.53 M ohms
    V0815 = 6.12 M ohms
    V1623 = 8.25 M ohms
    V2431 = 6.56 M ohms
    V3239 = 5.25 M ohms
    V4047 = 6.08 M ohms
    V4855 = 5.44 M ohms
    V5663 = 5.92 M ohms

    Double checked and all readings repeat to within .01 M.
  • VonSzarvasVonSzarvas Posts: 2,466
    edited 2019-08-15 14:27
    Is anyone else getting "open diode" when measuring those pins with diode multimeter setting? I found that on 2 of the VIO-to-GND pairs. Rest were close to either 1V or 2V.

    Edit: Scratch that. Might be the pin fet reacting to measurement voltages.
  • W9GFOW9GFO Posts: 4,007
    All of mine are between 18 and 20 Megs.
  • cgraceycgracey Posts: 13,627

    So, it looks, so far, like we don't have any ohmic connections between the VIOs and GNDs on any of the first-silicon chips.

    That's good!

    This suggests that something was just screwy in this last silicon run. The only change to the pad ring was the PLL filter settings, which wouldn't have had such effects, and only connects to V2431, anyway.
  • potatoheadpotatohead Posts: 10,218
    edited 2019-08-15 15:13
    I just saw this late Chip. I will get measurements for you later today when I am back home.
  • I could test 3 boards, 2 RevA with P2-ES packaged chips, and 1 RevB with a P2-v1-Globtop.
    All measure in the range of 1M to 5M. Mostly close to 3Mohms.
  • tomcrawfordtomcrawford Posts: 1,107
    edited 2019-08-15 15:54
    invalid data
  • Each one showed a starting rating as below, but quickly started to rise, beyond 25 Mohms:
    V0007 = 15- M
    V0815 = 14- M
    V1623 = 16- M
    V2431 = 14- M
    V3239 = 14- M
    V4047 = 15- M
    V4855 = 15- M
    V5663 = 14- M

  • And the lesser the current each kind of multimeter uses, in order to take resistance meassurements (thus, the higher the M Ohm scale it can reach), the longer the time each VIO pin will take to charge-up.

    Here, I've been able to repeatedly walk thru each 8-pin round, and did still found all the pins at higher than 6~7 MOhm, each turn. It's only a matter of doing it at a fast pace.

    So, at least in my EVAL board, P2 and surounding circuitry current leakage was found to be extremelly low.
  • You'd think after 70-odd years I would have learned to follow directions. Here's the readings at the 1x6 headers like you asked for:

    0007 2.5M
    0815 3.6M
    1623 2.7M
    2431 2.8M
    3239 1.9M
    4047 3.0M
    4855 3.0M
    5663 3.4M
  • cgraceycgracey Posts: 13,627
    Thanks, Everyone!

    It seems pretty certain that the original silicon didn't have any short issues on the VIO pins.
  • RaymanRayman Posts: 12,235
    I used a fluke 77 and got 4.3 to 6.1 MOhms on all supply pins with plus on pin and minus on ground.

    With leads reversed got 234 to 266 kOhms on all.
  • RaymanRayman Posts: 12,235
    Using diode mode they all read about 0.45 volts with minus lead on pin.

    With plus lead on pin, most read OL but some read ~1.5 volts
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