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PMB 688 Pin Assignment Inconsistency !!!! — Parallax Forums

PMB 688 Pin Assignment Inconsistency !!!!

Wael_ElEgyptianWael_ElEgyptian Posts: 3
edited 2011-05-18 12:38 in Accessories
I have just got my PMB688 Module and I noticed that the bads on the back of the PCB are inconsistent with those listed in the specification file posted for Parallax part#28501:
http://www.parallax.com/Portals/0/Downloads/docs/prod/sens/PMB-688_Specification_V0.1.pdf

Which one should I follow? Should I ignore what's written on the module and stick to the posted specification???

Your quick response is highly appreciated.

Best Regards,

Comments

  • FranklinFranklin Posts: 4,747
    edited 2011-05-05 07:33
    You might get faster answers by emailing support@parallax.com
  • Wael_ElEgyptianWael_ElEgyptian Posts: 3
    edited 2011-05-05 11:54
    Thanks Frank
  • PJAllenPJAllen Banned Posts: 5,065
    edited 2011-05-05 15:44
    Welcome to the Forum, Wael.
    I have one of these, PMB-688, and I'm very familiar with it.
    There is no discrepancy between the doc (linked) and the silk-screen (on my device.)
    N.B. - The device is depicted with the shiny metal case up and the antenna down.
  • PJAllenPJAllen Banned Posts: 5,065
    edited 2011-05-05 16:26
    Uh-oh!
    Looks like I'm eating crow tonight!

    Pin 4 is Ground blk
    Pin 3 is +V (5V) red
    Pin 2 is "RX" blu
    Pin 1 is "TX" yel

    wht and grn are not conn'd (as far as I know.)
  • PJAllenPJAllen Banned Posts: 5,065
    edited 2011-05-05 16:35
    Here's what's "funny" -- the pads and thier silkscreened labels, on the antenna side, do not correspond to the pins of the connector, spatially. I confirmed this with the ohmmeter. The pad labelled "GND" has continuity to pin4 (black wire), "VIN" has continuity back to pin3 (red wire), "RXD" has continuity back to pin2 (blue wire) and "TXD" has continuity back to pin1 (yellow wire).

    So, I get a reprieve from that crow dinner.

    PE - When I wired mine up, I just went with the wiring presented on the pdf (your doc as linked) and gave no consideration to those pads or their labels.

    attachment.php?attachmentid=74691&d=1287966608
  • Jorge PJorge P Posts: 385
    edited 2011-05-18 10:41
    Please see this post from Chris Savage, http://forums.parallax.com/showthread.php?119317-PMB-648-GPS-Part-28500-Wrong-Datasheet&p=874298&viewfull=1#post874298 the datasheet is correct but the lableing on the device is wrong as it is a multi layer board!! It should be the same with PMB 648 and 688...
  • PJAllenPJAllen Banned Posts: 5,065
    edited 2011-05-18 12:38
    The pads on the PMB-688 are labelled correctly.
    The order of those pads does not correspond to the layout of the pins in that connector.

    The assumption that the pad labels correspond to the order of the pins is invalid.

    The pins as depicted/presented in the documentation linked are accurately rendered.
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