Can FMC_NOE used as Clock?

[Benjamin Gao]

Posted on June 27, 2016 at 05:17

Hello eveyone.

I'm using a STM32F746 to drive two AD7606s under FMC NOR-flash mode, to read the AD's data, i need to put a nRD signal into the AD7606, and FMC_NOE is chosen for it. The nRD signal shall be 15ns low and 16ns high, i don't know if FMC_NOE under FMC mode is capable to reach  such a high freq. Also this come to me with a question that if any GPIO pin in any mode can reach the highest freq(like 260MHz) in STM32F746 ?Thanks a lot~

[troy1818]

Posted on June 27, 2016 at 11:10

Hi  there,

There is no problem for a pin to reach the freq you are looking for (but ceartinly not 260Mhz, what spec have you been reading?). Sure, you will have a little trouble reaching high freq with just setting a pin to output mode and start toggle it with code. However, setting a pin to alternative function is a whole different story.As to the question whether or not you can use FMC_NOE as input clock, I cannot say for sure but I would be surprised if it did not work. It really depends on the input characteristics for the pins you want to clock, pcb layout and how exact you need to clock signal to be, to mention a few.Regards,/Rygelxvi

[Benjamin Gao]

Posted on June 28, 2016 at 06:32

Thank you rygelxvi, the highest freq is 216MHz, i got it wrong.

Now i take the parallel way to process, fmc is configured to NOR flash mode?with one chip-select FMC_NE1, one FMC_NOE,one FMC_NWE, one FMC_A0 and 16bit data bus FMC_[0:15]: 1. FMC_NE1 control two AD7606s, one of them take neg2. FMC_NOE as high speed read enable to AD's nRD pin3. Two AD share the data bus4. FMC_NWE and FMC_A0 left unusedI hope this will work

[troy1818]

Posted on June 28, 2016 at 12:18

You really need to look at the timings for the AD7606 and match it to the NOR operation for stm32 to understand if it will work or not. Make sure that all timing constraints in figure 4 are fulfilled. 66 Mhz will never work. I think you mean 33Mhz which is absolute maximum for the AD chip (t11).