Messages in this thread | | | From | Andy Shevchenko <> | Date | Mon, 25 Jul 2022 22:41:31 +0200 | Subject | Re: [PATCH 1/2] gpio: gpio-74x164: add support for CDx4HC4094 |
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On Mon, Jul 25, 2022 at 3:54 PM Linus Walleij <linus.walleij@linaro.org> wrote: > > On Mon, Jul 25, 2022 at 11:32 AM Andy Shevchenko > <andy.shevchenko@gmail.com> wrote: > > On Thu, Jul 21, 2022 at 11:32 AM Marcus Folkesson > > <marcus.folkesson@gmail.com> wrote: > > > > > > 74hc4094 and 75hc4094 works similar to 74x164 but has an additional > > > storage latch associated with each stage for strobing data from the > > > serial input to parallell buffer tri-state output. > > > > parallel > > > > > Add support for an optional strobe pin. > > > > Sorry for my absence of understanding, but why? > > SPI has MOSI, CLK, CS, where the last one is exactly for that. No? > > Forgive me if I misunderstand, but if you use CS that > way, the way that the SPI framework works is to assert > CS then transfer a few chunks over SPI (MOSI/CLK) > then de-assert CS. > > If CS is used for strobe, it is constantly asserted > during transfer and the sequence will be latched > out immediately as you write the SPI transfers and > the data is clocked through the register, making the > whole train of zeroes and ones flash across the > output pins before they stabilize after the SPI > transfer is finished. > > If you first do the SPI transfer, then strobe after > finished, this will not happen. > > Then it should be a separate pin, so this doesn't > happen, right? > > Yours, > Linus Walleij
-- With Best Regards, Andy Shevchenko
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