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TMS320F28375D: TMS320F28375 USB Host Function.. Pulldowns on DP/DM..

Newman
Expert 6005 points
Part Number: TMS320F28375D
Other Parts Discussed in Thread: TMDSCNCD28379D, C2000WARE

Hi Team C2000,

What collateral/schematics do we have available for example TMS320F28375D USB Host Hardware Design? 

With F28 acting as a USB host, are separate/external 15K pulldowns required on DP/DM?

Thanks, Merril 

  • 0
    TI__Mastermind 45426 points

    Hi Merril,

    The TMDSCNCD28379D (ControlCard) is documented as supporting both USB host/device connectivity through J8. Pull-downs are not included on the DP/DM lines of the board however.

    Reviewing the USB 2.0 spec, it seems like the pull-downs are only necessary for 'Low-/Full-speed Device Speed Identification' specifically.

    There are a number of C2000WARE examples the host case has and can be tested with to give you some confidence. Directory below:

    C:\ti\c2000\C2000Ware_3_03_00_00\driverlib\f2837xd\examples\cpu1\usb

    Best,

    Kevin

  • 0 in reply to Kevin Allen18
    TI__Expert 6005 points

    Hi Kevin,

    Thx. I'm trying to ask some specific questions here to better understand the USB pull situation.. can you please answer each specific question below?  Thx!

    For a USB2 full-speed spec-compliant setup, It seems that the host is required to have pulldowns on DP/DM and the (full-speed) device must pullup DM (to indicate that it (the device) is full-speed).. correct?

    Specifically for a (say MSP) full-speed device connected to a (say C2000) host, should this be implemented as follows?

    -Host Side (c2000) pulldowns of ~15K on both DP & DM

    -Device Side (MSP) pullup of ~1.5K on DM

    Since the C2000 EVMs do not have pulls.. are the C2000 internal pulls used in our (TI) example code/projects?

    If C2000 is a USB host and there are no external pulls & no internal (c2000) pulls enabled.. seems DP/DM will be floating.. so what will happen?

    Thanks, Merril

  • 0 in reply to Newman
    TI__Mastermind 45426 points

    Hi Merril,

    Sure, I need look into this some more and check a few things before answering. I'll get back to you tomorrow on this.

    Thanks,

    Kevin

  • 0 in reply to Kevin Allen18
    TI__Mastermind 45426 points

    Hi Merril,

    I believe the USB module has internal pulls to meet the spec requirements. The USB section of the TRM mentions the transaction process being automatically handled quite a bit, like below:

    I'm going to confirm with the team and get back to you.

    Best,

    Kevin

  • 0 in reply to Kevin Allen18
    TI__Mastermind 45426 points

    Hi Merril,

    Confirmed with the team, external pulls are not needed on your board. The C2000 USB module takes care of the pull requirements documented in the USB 2.0 spec.

    Best,

    Kevin

  • 0 in reply to Kevin Allen18
    TI__Expert 6005 points

    Hi Kevin,

    Thx! 

    Do you know if the pulls are automatically included/on (just when USB mode is enabled)?  or..

    Do the sample projects turn the pulls on?  or..

    Do we need to specifically & explicitly turn the pulls on for the GPIOs?

    Thx, Merril

  • 0 in reply to Newman
    TI__Mastermind 45426 points

    Hi Merril,

    The user does not need to turn the pulls on themselves. The user just needs to configure the USB module and signals as we document in the TRM section. The pull requirements of the USB 2.0 spec will be taken care of internally by the C2000's USB module based on the set Host / Device mode and protocol.

    Best,

    Kevin