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AM263P4-Q1: boot mode circuit and QSPI flash for custom board

Guillermo Gutierrez
Prodigy 35 points
Part Number: AM263P4-Q1
Other Parts Discussed in Thread: LP-AM263P, SN74AVC4T245, TMDSCNCD263P

Tool/software:

Looking at the evaluation boards TMDSCNC263P and the launchpad LP-AM263P, they use a bus transceiver (SN74AVC4T245) and a delay for connecting the boot pins a little time after PORz  goes high so the MCU reads them, and then the boot circuit goes to high impedance. Why it is needed if the pins are push/pull type?. Can I just connect pull up/pull down resistors directly  to the OSPIO_D0/D1 lines for my custom board ?.

Looking at the hardware guidelines (SPRABJ8C) mentions "The OSPI Flash memory interface is the primary bootloader memory location for the AM263Px and AM261x MCUs" , but in the TMDSCNC263P you have both QSPI and OSPI. Is ti possible to have in my custom board only the QSPI?

Thank you

  • 0
    TI__Expert 8536 points

    Guillermo,

    Guillermo Gutierrez said:
    Can I just connect pull up/pull down resistors directly  to the OSPIO_D0/D1 lines for my custom board

    Using the directional bus transceiver is highly recommended:

    1. It ensures proper direction (A->B in this case being from the bootmode switches/pull resistors to the SOP pins)
    2. It holds the bootmode selection and SOP inputs at the same logic level
    3. It ensures the timing requirement relative to PORz is met and the device can boot sequence properly 

    In addition, a method of isolation is required between the SOP Bootmode nets and the functional OSPI/SPI nets. On the TI EVMs, this is accomplished via 10k resistors as close to the AM26x as possible on the SOP[3:0] nets. For the TMDSCNCD263P, these are R119, R122, R150, R151.

    Guillermo Gutierrez said:
    Looking at the hardware guidelines (SPRABJ8C) mentions "The OSPI Flash memory interface is the primary bootloader memory location for the AM263Px and AM261x MCUs" , but in the TMDSCNC263P you have both QSPI and OSPI. Is ti possible to have in my custom board only the QSPI?

    Yes - however, in order to boot from the QSPI, you must connect the QSPI device to OSPI0_CS0. The boot rom is not configured to allow boot from an OSPI/QSPI device connected to OSPI0_CS1.

    Regards,

    Brennan

  • 0 in reply to Brennan Hartigan
    Prodigy 35 points

    Hi Brennan, Our custom board will not have a Test Automation header, basically the boot pins will be set when the board is off, I was thinking something like the picture below where the AM263P_SOPx will be connected to 3 pin headers with one side to MCU 3.3V and the other to GND, so with a jumper can be selected. That means the AM263P_SOPx signals are connected to a known voltage all the time.

    But it is only possible if the AM263P_SOPx will not interfere with the AM263P_OSPIDx signals, where I am thinking it shouldn't because they are push pull type, so any pull up or pull down will not affect the communication between MCU and memory.

    What could be the problem with this?

    Thank you

  • 0 in reply to Guillermo Gutierrez
    TI__Expert 8536 points

    Guillermo, 

    Yes, it is ok to have the SOPx signal connected directly to the AM263Px without the directional bus transceiver. However, it is included in all TI EVM designs and most of our customers use this implementation, even without a test automation interface. It guarantees the correct timing and logic level of the bootmode/functional pins. You must meet the timing requirement of the SOP state being held for at least 20ns after PORz low to high transition for bootmode to be latched in correctly.

    However, like I mentioned, you need the 10k isolation resistors in order to isolate the boot mode from the functional mode of the SOP pins. 

    Regards,

    Brennan

  • 0 in reply to Brennan Hartigan
    Prodigy 35 points

    Hi Brennan, In case we play safe and decided to use the buffer, it doesn't need to be dual rail/voltage translator, right? Because when PORz de-asserts, the MCU 3.3V is already good,  then the buffer could  be  feed only with this one. Is that right?

  • 0 in reply to Guillermo Gutierrez
    TI__Expert 8536 points

    Guillermo,

    That is correct. When PORz goes high, 3V3 is already ramped.

    I would highly recommend you go through the AM26x Hardware Design Guidelines document, and the AM26x Custom PCB System Getting Started Guide (for when your design is complete and you are ready to bring up your board). Please let me know if you have any additional questions.

    Regards,

    Brennan