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i.MX6 ECSPI slave: Maximal SCLK frequency (fast / slow group)

Question asked by Eli Billauer on Jun 28, 2017
Latest reply on Jun 29, 2017 by Eli Billauer

Hello,

 

I'm trying to figure out the maximal ECSPI frequency as slave in read mode on an i.MX6 device. According to the datasheet [1] (section 4.11.2.2), the max frequency depends on whether the relevant pin is in the fast or slow group, and the footnotes outline which is which.

 

But I suspect that the list given in section 4.11.2.2 (slave timing) is wrong. Here's why:

 

Let's look at section 4.11.2.1 of the datasheet, which gives the timing for master mode. The ECSPI pins listed there in footnotes 1 and 2 are candidates for MISO pads, which makes sense: The data rate depends on whether the data input pad is in "slow" or "fast" group (whatever that means).

 

When switching to slave mode, the MISO and MOSI pins swap directions, so I would expect other pins (i.e. the MOSI candidates) to be enlisted in the footnotes to the timing spec for slave mode. But they are the same pins as in master mode. So according to 4.11.2.2, the maximal frequency for reading depends on the choice of the data output pins, which makes no sense.

 

Specifically, I'm going to use EIM_D22 as MISO and EIM_D28 as MOSI. According to footnote 2 of Table 52, EIM_D22 is listed as a fast pin, so I should be allowed to run at 25 MHz (40 ns). But again, it doesn't make sense to me that this decision depends on EIM_D22 = MISO, which functions as an output from the i.MX6 device in slave mode.

 

Insights are highly welcome.

 

Regards,
   Eli

 

[1] https://cache.freescale.com/files/32bit/doc/data_sheet/IMX6DQCEC.pdf

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