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Question on external USB circuitry from MSP430

Yousef Debs
Prodigy 80 points

Hello,

As found in SLAA458, the revised pulseoximeter application, I've attached an image of the USB schematic that is used to output collected data. I just had a few questions about this schematic.

 

1) What do J3 and J6 correspond to? I can see the corresponding node names on the Ft232BM chip on J3, but these two are not present in any other schematic of the project. Is this simply a 7-pin header used to tidily connect components to the chip?

2) In the lower left hand side of the schematic, there are two connections labeled IC2P with pin numbers going from ground or vcc. Does this simply mean pins 26 and 3 need vcc while pins 17 and 9 need to be grounded?

3) Is there some special assembly required for the 6Mhz crystal or should it just be very carefully soldered to pins 27 and 28?

 

Thanks and best regards,

Yousef. 

  • 0
    Guru 227245 points

    1) Yes, J3 and J6 are just pin connectors with the named signals on them. If you have a BOM for this schematic, it may list package information. But most likely these are just breakout pins.

    2) Yes. The chip likely has more than one VCC/GND pin. Many higher-integrated chips have, to allow easier bonding inside. Or to prevent voltage drops because of higher currents through the thin internal bonding.

    3) Yes again. Crystal layout is a difficult thing. There are soem threads abotu this in this forum. Basically: avaoid anything near teh crystal and its connections to the chip that can form parasitic (and even more unbalanced parasitic) capacitances, as well as signals that can crosstalk to (or from) the crystal.

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