Electronics > Microcontrollers

Do any SPI chips clock data in on a +ve clk edge, but require clk parked at 1?

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peter-h:
It would seem to be a weird sort of logic design to really require that.

It is SPI Mode 3.

In recent years I have done code for various SPI chips and never found this was needed, and Mode 0 was just fine.

jpanhalt:
I don't have much experience, but in one instance I used mode 3.  I like the ST75xx displays (e.g., ST7525 and ST7576).  They are fast enough for my needs, and I am comfortable with them.  In my experience, they work with modes 0,2, and 3, but not mode 1.  MCU is an enhanced mid-range PIC 16F1xxx at 8 MHz or 16 MHz usually.

In a recent project, I used the MAX31856 TC amplifier.  That worked with modes 1 & 3 only, so I ended up using mode 3.
 
I have not seem any device that only works on mode 3.

peter-h:
ST7525 is a great example of what I believe must be a BS data sheet:



Same with STLED316:



How can the clock parked HIGH be possibly relevant? It "must" also work in Mode 0. The STLED316 definitely runs fine with Mode 0. In fact if using Mode 3 for it, I found that mucks up some other devices on the same SPI, although that it almost certainly an artefact of re-initialising the STM 32F4 SPI between devices (it doesn't like it much).

jwet:
Over the years, I think all permutations of CPHA and CPOL have been used.  In a lot of cases, its a don't care since the clock is edge triggered and the resting state doesn't really matter.  True SPI will operate in mode 0 but these synchronous ports on micros have to support a lot of non standard stuff.  If you look at shiift registers, '299 or '595- they can be odd.  National "microwire" is SPI adjacent but not consistent- it also has active high CS.  Dallas DS1620 and other parts have a odd SPI like interface with clock and a combined data I/O.  Sometimes there's an extra inversion involved like going across an opto-coupler barrier and its convenient to untangle it in software.  Maxim made ADC's and DAC's that had varying CPA and CPOL before things got relatively standardized.  The MAX512/3 DAC's had an odd SPI like interface.  Standards aren't so standard.

IDEngineer:
In other words: "The nice thing about standards is there are so many different ones to choose from."

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