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SPI usage


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#1 Wernfried

Wernfried

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Posted 04 January 2015 - 09:14 PM

I'm new using SPI, may be I'm doing it totally wrong.

 

I need to switch an RF device and I figured out how the code looks like. One short pulse has to be 250s. Sending the code using a parallel port together woth a Delay functions works well.

 

Since the Delay Loop in .Net can be interrupted I had the idea using the MOSI of the SPI to generate the code. Thus I implemented a short test, but is seems the code is sent to fast. Thats why I made the following test:

 

The SPI config is the following:

            SPI.Configuration rcConfig = new SPI.Configuration(
                Pins.GPIO_PIN_D8,
                true,
                0,
                0,
                false,
                false,
                4,
                SPI.SPI_module.SPI1
            );

I declared a clock rate of 4KHz, which is a 250s cycle. Then I send 1000 byte

            byte[] xxx = new byte[1000];
            for (int i = 0; i < 1000; i++) xxx[i] = 0xaa;
            spi.Write(xxx);

On the MOSI port (11) I expect a signal for about 2 seconds (1000 Byte x 8 bit x 250s), but it is much lesser then a second.

 

Where is my fault? Does 4KHz mean, one Byte is sent within 250s and not one Bit as I expected?

How can I send a code with a duration of 250s for one bit?

 

 



#2 Wernfried

Wernfried

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Posted 07 January 2015 - 10:55 AM

I found another topic which explains my problems.

 

http://forums.netdui...ossible-speeds/

 

According this explanation I think my fault was to assume the clock rate is 4KHz. The lowest available clock rate is 164 KHz on APB1 and 328 KHz on APB2.

 

In that topic I could figure out the available frequncies for SPI1, SPI2 and SPI3.

Since APB1 allows a lower clock rate I would use either SPI2 or SPI3.

 

Now my question ist, on what port can I access MOSI of SPI2 or SPI3? For SPI1 it is somewhere explaned (Port 11). But I cannot find any hints where MOSI for SPI2 or SPI3 is available. Is this avalable at all?






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