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ADuC706x max. SPI bitrate in slave mode

Question asked by m.teichgraeber on Apr 22, 2016
Latest reply on Apr 26, 2016 by MMA

On page 97 of the datasheet it is written that the "slave accepts data from an external master up to 5.12 Mbps." This appears to conflict with the minimum value of the data input hold time tDHD, on page 13, table 5, which is specified as 2 x tUCLK. Given that tSL must be at least tDHD (minus the duration – which can be negative – SPI masters keep the data valid on the MOSI line after the output changing SCLK edge),  the clock period may not be shorter than

2 x tDHD = 2 x 2 x tUCLK ≈ 391ns which results in a max. bitrate of 2.56 Mbps. This is only half of the value given on page 97.

 

If I am not doing something wrong in my calculation, which of these max. frequency values is the correct one?

The ADuC7061 (at least the piece that I'm testing), by the way, appears to accept data even at 7.5MHz, which suggests a smaller minimum tDHD value.

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