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TMS320F28377D: RNW signal on the C2000 series

Takayuki Mori
Prodigy 80 points

Part Number: TMS320F28377D
Other Parts Discussed in Thread: TMDSDOCK28379D

I'm currently considering accessing an external memory area using the parallel bus with the C2000 series, and I have the following question:

Which of the following is the output logic (Hi/Lo) of the RNW pin?

CASE 1:
  READ: Maintains Hi
  WRITE: Emits a Low pulse with the same width as CS

CASE 2:
  READ: Emits a Hi pulse with the same width as CS
  WRITE: Maintains Low

CASE 3:
  Other than the above (please advise)

Is this behavior common across the C2000 series?

For example, do the XR/W~ and EM1RNW pins function the same on the TMS320F283335 and TMS320F28377D?

Regards,

T. Mori

  • 0
    TI__Mastermind 24711 points

    Hi Takayuki-san

    You can specifically refer to the EMIF user guide as it is very detailed for this purpose: https://www.ti.com/lit/pdf/sprac96 . Case 1 is the accurate representation of the signal, maintaining Hi for Read and pulsing Low for Write

    The XR/W from the XINTF perihperal and EM1RNW from EMIF peripheral should function the same, XINTF is just older peripheral and EMIF has some optimizations and improvements so we recommend to use that (also because it is available in our newer devices like F28P65x family). 

    You can see this for example displayed in the datasheet

    Regards,

    Peter

  • 0 in reply to Peter Luong
    Prodigy 80 points

    Hi Peter

    Thank you for your reply.

    You said that CASE 1 was correct, and I thought so too, since the diagrams in the datasheet and other documents look like that.
    However, when I checked the waveforms on an oscilloscope using TI's TMDSDOCK28379D evaluation board, it was the opposite, CASE 2.

    CASE 2
    READ: A high pulse of the same width as CS is output.
    WRITE: Maintains low.

    Why is this happening? Is there something wrong with the board or settings?
    Note that the internal pull-up is enabled in the GPIO pin settings.
    I also tried attaching an external pull-up resistor to the board, but there was no change.
    (Could there be some reason for the signal being pulled low?)
    The board is running standalone, with nothing connected (nothing connected to the RNW pin).

    Please confirm again and reply.

  • 0 in reply to Takayuki Mori
    TI__Mastermind 24711 points

    Hi Takayuki-san,

    This is strange that you are seeing the opposite case. There is a note that it may be required to invert the RNW signal as below

    "Asynchronous memories that support CS controlled operations can enable the Select Strobe mode and use RNW to directly control WE and externally invert RNW to control OE"

    Is it possible for you to test this with an external memory device? I think in standalone it will be harder to check the EMIF unless it is actively being interfaced.

    Regards,

    Peter