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Multilink MC908QG8 connection problem - urgent need help
Paul S. Aug 23, 2015 at 11:09 AM (11:09 hours)
Staff: Takao Y.

  • Hi We have a rev. C USN Multilink. P/N is USB-ML-12E. We have been using it several years successfully with a custom designed eval board that has a MC908QG4 part. It has wire wrap headers and a 3 volt regulator board. Recently I changed the part to a MC908QG8. With the latest version of CodeWarrior open when I connect the 2x3 connector from the Multilink the blue LED is on but the yellow flashes on for a half second and goes out. When I try to flash the part CodeWarrior says there is a connection error. I have changed the QG8 part several several times and the yellow LED never stay on solid. I have verified 3 volts on the BDM connector on the board. We are right in the middle of a project and urgently need help.

    Thanks,

    Paul




    Comments

  • Greetings,

    The yellow LED going out is worrying. As you may know, that indicates power being detected on your chip. Do a comparison of two scenarios:

    1) Measure the voltage (pin 6 and pin 2) on the BDM without the multilink connected.
    2) Measure the voltage on the BDM with the multilink connected.

    Does the voltage drop when the multilink is connected?
    Does your circuitry have any current-limiting resistor on VDD? If so, you may want to reduce this value to allow more current. The multilink needs roughly 0.2A to power up a few buffers internally as a voltage reference.

    Also measure the BKGD and RESET voltages as well. If they do not match the voltage on VDD, then you need to check your schematic to see what is drawing current and dropping the voltage.


    Takao Yamada

  • Greetings, 

    I measured both pin 6 and 2. I observed no voltage drop when the multilink was connected. The BKGD and RESET pins are connector to header pins that are not connected.

    The curious thing is that I have been using these boards with the QG4 for years with no issues. It seems only when a QG8 was installed the yellow light did not come on. The 3.0V Vdd did not change with the multilink connected or disconnected.

    We are using the QG8 in a new design. Since the multilink draws .2A should we use a higher current regulator? I believe

    Looking forward to your response.

    Thanks,

    Paul

  • Greetings,

    I am not understanding your statement "The BKGD and RESET pins are connector to header pins that are not connected." Are you saying that BKGD and RESET are not connected to your BDM? Could you clarify this?

    So even when the yellow LED is off, you still measure 3V. That is odd.

    If you switch back to QG4 with this multilink, will it work today? Can you confirm this so that we know the multilink is still in good condition?


    Takao Yamada

  • Greeting,

    Please excuse the comment about the BKGD and RESET pins. They are connected to the part through the 2 x 3 BDM connector. All off the port pins of the processor are brought out to wire wrap pin headers none of which are connected to any load.

    I do have another board with a QG4 on it and the yellow LED does come on.

    I will measure the voltages on the BKGD and RESET pins and respond shortly.

    Question... What current spec should I use for the 3V voltage regulator?

    The one on the board is a 150ma part.

    Thanks,

    Paul

  • Greetings,

    I check the board that does illuminate the LED.

    Pins BDM not connected BDM connected

    RESET 2.9V .43v
    BKDB 0V 0V

    This is quite a difference.

    Looking forward to your comments.

    Thanks,

    Paul

  • Greetings,

    Correction, the multilink needs 0.02A, or 20mA.

    Reset and BKGD both needs to be near 3V when the multilink is physically attached to the target. The moment you use Codewarrior to connect, the multilink drives reset low. This is what you are seeing with 0.43V. This is actually fine. But the big problem is the 0V BKGD reading. The multilink can only pull down and release the BKGD line so if it is already at 0V then there can not be any communication to the part.

    Check your schematic and ensure that BKGD is a direct connect from the chip to the BDM header. One thing you may want to try is putting a pull-up resistor of 4.7K-10K Ohm on BKGD line to help pull it up to 3V. This could be another indication of current-limitations that you may have on your board that is not allowing enough juice for the chip and the multilink to work properly.

    My suggestion is to remove any current-limitations and just see if you can connect to your chip.


    Takao Yamada

  • Greetings,

    Good to hear the multilink only requires 0.020ma. More than that would have changed our design.

    I just erased and flashed another project board with a QE64 part
    without any problem so the Multilink is working.

    The voltage regulator on the eval board can supply 150ma. at 3V and I see no indication of any over current condition.

    I will add a pull up resistor to the BKGD pin. Will let you know how it works.

    Thanks for your support.

    Paul

  • Greetings,

    I added a 6.8K pull up from 3V to the BKDM pin. Did testing on board with the QG4 and QG8.

    QG4 no multilink multilink connected
    Reset 2.7V .45V
    BKGD .018V .024V

    QG8
    Reset 2.7V 2.7V
    BKDB 3.0V 3.0V

    I believe one of these parts are damaged.

    Thanks,

    Paul

  • Greetings,

    Wait, so you are saying the QG8 is now behaving better than the QG4? Because the QG4 looks to have no BKGD voltage while the QG8 did.


    Takao Yamada

  • Greetings,

    Those are the voltage readings. CondeWarrior could not communicate with either part. I have ordered a Freescale demo board and QG8 daughter board. I am sure we will get the part working with it.

    We also ordered a 16 pin DIP QG8 package and will wire wrap a BDM connector on some vector board and try to see if it works.

    Is the external pull up necessary? I have never used one in my design and the data sheet show an internal PU on Reset and BKGD.

    I suspect the QG4 board has a bad part on it even though the yellow LED is on. As I said I did re-flash another project board successfully so we know the Multilink is working. I have no idea why a ne QG8 part did not work. The ones we are using are in a QFN package and difficult to hand solder.

    Regards,

    Paul

  • Greetings,

    Even though the chip does have an internal pull up on Reset and BKGD, an external pull up is only necessary if the rise-times are too slow. I would agree the demo boards will work perfectly (because we designed it), and it would be a good way of knowing if your setup works. Also you can take a look at the schematic design of the demo board and find out if there are any recommended design you should implement into your board.


    Takao Yamada

  • Hi Takao,

    I have received the Freescale demo board and the QG8 daughter board. Will try to get them set up in a few days. Also have some QG8 DIP parts, an IC socket and a 2 x 3 header I will wire wrap later this week and see if we have the same problem with the yellow LED. I suspect the parts on my custom designed demo board were bad.

    Will let you know how things turn out.

    Thanks,

    Paul

  • Greetings,

    Any update on this?


    Takao Yamada

  • Hi Takao,

    No update. The board seems some what consistent. It changes from 10.0Hz to 9.6Hz.
    Only those two values. Since this is driving a divider chain I do not think the accuracy for our purpose will be an issue.

    Thanks for all of your help.

    Regards,

    Paul

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