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TMS320F28075 - PZP 100 pin package - Booting via the SCI

chris moir
Intellectual 400 points

According to the pinout info (SPRS902B), GPIO72 (pin 80) needs to be low, GPIO84 (pin 85) needs to be high, and TRST needs to be low (via a pulldown resistor).  The boot sequence is reset, send in "A" to set baudrate, and then download a hex file to the SCI.    In the PZP package, the default SCI IO pins are GPIO85 (pin86) and GPIO84 (pin 85).  i.e. a clash.

Any idea how to deal with this?

Can anyone point me to a hardware solution?

 

  • 0
    TI__Guru 57255 points

    Hi Chris,

    You are correct, however there is not contention.

    During bootloading, GPIO84 will look at its status (and you'll need to pull it high).  It will only need the status of the pin during boot though.  After it enters the SCI bootload code, the pin will then get used as SCI-TX.  It will then drive (echo) to an external host. 

    In summary: The net including GPIO84 will therefore only ever have one driving source, the C2000 itself - and it will only come on after determining the boot mode.  Before, it will get pulled by the external resistor.

    If you would prefer to completely decouple things, you could change the GPIOs used as boot mode pins by programming the OTP (when you program your boards at your factory). 

    ===

    In case you were not aware, there is a free Windows program called C2Prog which can be used to program the flash of a C2000 via SCI/UART.  It may be interesting if bootloading is not something you want to spend time on and you just want something that will work.


    Thank you,
    Brett

  • 0 in reply to Brett Larimore
    Intellectual 400 points
    Hi Brett,

    Thank you for your rapid and welcome response - I was sure that there was a way through, but hadn't thought of dual use of one of the pins - a nice piece of design!

    We are prototyping a dual 28075 CPU for a new laser-based sensor for high performance cars, measuring velocity, slip, suspension height and attitude. It all fits into a 60 mm diameter "pot", and drives a CAN bus. A nice toy!

    Thanks again,

    Chris
  • 0 in reply to chris moir
    TI__Guru 57255 points

    That sounds like an interesting project.  I wish you much luck in your development!

    -Brett