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TDA3x EVM questions regarding GPMC(NOR Flash) interface..

Ernest Cho
Expert 3191 points
Other Parts Discussed in Thread: SN74CBT16214

Hello Champs,

One of my customer questions regarding TDA3x.

1. The TDA3x EVM schematic(Rev_C1) shows pull-down resistors for GPMC Address bus between NOR Flash(S29GL512S) and SN74CBT16214(Mux IC).
    For A0~A11 don’t have pull-down resistors, for A12~A17 have 10K R, for A18~A25 have 1K R.
    What is the intention of those R? Why A12~A17 lines and A18~A25 lines have different values of resistors?
    (The case of TDA2x EVM there have 10K R from A12~A25.)
    If the pull down R need for holding low when Mux IC output is high impedance, then, why there’re no pull-down R for A0~A11? (for both TDA3x and TDA2x board?)

2. instead of S29GL256S10, can they use M29W256GH70N3E for NOR Flash?

3. Is there any method without using multiplexer at the GPMC for reducing their BOM? Because GPMC pins are only used at the booting period, most of the time they may be used for VOUT1.

Thanks,
Ernest Cho

  • 0
    TI__Prodigy 170 points

    Hello Ernest,

    1. If GPMC address signals do not go through on-board multiplexors, external pull-down resistors are not needed. All TDA3x GPMC_A[27:0] pads have internal pull-downs enabled by default at reset. It could be noted here that since ROM code initializes (by selecting GPMC mux mode) and actively drives address lines GPMC_A[19:0] only, the higher-order addresses are passively held in logic low by these IPDs. For avoiding any risk of noise pick-up and so of false addressing at boot, external pull-down resistors can be used for strengthening the IPDs on GPMC_A[n:20]. This is not mandatory though and depends on the particular design and EMI environment.

    2. The suggested Micron part would work without problems. It is CFI-compliant as well, and asynchronous non-muxed parallel NOR flash is fairly standard in general.

    3. Generally possible. Measures must be taken in software though to make usage of TDA3x pads as GPMC and as VOUT1 mutually exclusive if ever run-time access to the NOR flash would be required (e.g. for software update).


    Regards,

    Lubo