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18F252 with RFM42B - hardware SPI

 
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madmax



Joined: 15 Nov 2011
Posts: 2

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18F252 with RFM42B - hardware SPI
PostPosted: Tue Nov 15, 2011 8:50 am     Reply with quote

Hello.

Sorry for my bad English.

My problem:
I am trying to connect the CPU PIC18f252 with module RFM42B using hardware SPI. However, I have no response from the RF module.

1)
- I set the CPU clock 20MHz
- setup_spi (spi_master | spi_l_to_h | spi_clk_div_64)
- I set SDN at low level
- I set the SEL at low level
- spi_write (0x01)
- Result = spi_read ()
- I set a high-level SEL

I always get the result = 0

2)
- I set the CPU clock 20MHz
- setup_spi (spi_master | spi_h_tol | spi_clk_div_64)
- I set SDN at low level
- I set the SEL at low level
- Spi_write (0x01)
- Result = spi_read ()
- I set a high-level SEL

I always get the result = 0

When I set the level of SDN High - result = ff

Software SPI is working correctly - result always wynik = 06 is correct

Where I make mistake?

http://www.hoperf.com/upload/rf/RFM42B_43B.pdf
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Piotr
PCM programmer



Joined: 06 Sep 2003
Posts: 21708

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PostPosted: Tue Nov 15, 2011 1:14 pm     Reply with quote

Here is the data sheet:
http://www.hoperf.com/upload/rf/RFM42B_43B.pdf

Look on page 3. It shows the SPI timing. It shows that SCLK idles at
a low level and samples the data on the rising edge. This is SPI Mode 0.
You should add the following #define statements above main() and edit
the setup_spi() statement so it uses Mode 0. Example:
Code:

#define SPI_MODE_0  (SPI_L_TO_H | SPI_XMIT_L_TO_H)
#define SPI_MODE_1  (SPI_L_TO_H)
#define SPI_MODE_2  (SPI_H_TO_L)
#define SPI_MODE_3  (SPI_H_TO_L | SPI_XMIT_L_TO_H)

//========================
void main()
{
setup_spi(SPI_MASTER | SPI_MODE_0 | SPI_CLK_DIV_16);
.
.
.



Quote:

Result = spi_read ()

I always get the result = 0

This line will not produce the SPI clock, so it will not clock in the new data.
You need to add a 0x00 parameter to tell it to make the SCLK signal.
Example:
Code:

result = spi_read(0);
madmax



Joined: 15 Nov 2011
Posts: 2

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PostPosted: Wed Nov 16, 2011 12:33 pm     Reply with quote

Thank you for help. Communication works. I did not know spi_read does not generate the clock signal Rolling Eyes.
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Piotr
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