Arduino Uno SPI CS pin goes low every 20ms

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i'm initialising rfm22 434mhz chip (https://www.sparkfun.com/datasheets/wireless/general/rfm22.pdf) on spi using radiohead library (http://www.airspayce.com/mikem/arduino/radiohead/)

it uses spi , can see on scope of spi pins work expected, , indeed chip intialises correctly.

what's odd if change time scale on scope say, 10ms per division, can see spi cs pin going low every 20ms. seems regardless of whether sketch doing anything, , repeats if sketch in blocking delay() function several seconds.

my guess i'm misunderstanding spi, expect go low when radiohead library making spi call. can explain i'm seeing? googling hasn't thrown many results.



Arduino Forum > Using Arduino > Networking, Protocols, and Devices (Moderator: fabioc84) > Arduino Uno SPI CS pin goes low every 20ms


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