Ruth Hendrix

Spi on HSC12C

Discussion created by Ruth Hendrix Employee on Jan 26, 2006
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Posted: Thu Feb 03, 2005 3:37 pm  
Hi all,

I'm a newbe here, so I thought I should try my luck
solving a basic simple problem of mine.

I have configured two controllers, HCS12C128, to communicate on the SPI. One as master, and the other as slave.

My problem is that I can't figure out how to return data from the slave.
I read the status register and then write to the data register, as the manual says, but I always receive the previously transmitted data in the master.

Thanks in advance,
Posted: Fri Feb 04, 2005 8:02 am    
I had forgotten to set the CPHA-bit. Embarassed
Posted: Fri Apr 22, 2005 4:54 pm    
Glad you found your solution. Strange thing is, I'm having the same problem, but I have the CPHA bit set. As far as I can tell, I have the other registers set where they need to be as well.

How did you set your other SPI registers? I'm thinking I might be missing a bit setting somewhere.

Posted: Mon Apr 25, 2005 6:16 am    

I keep the slave pulled down all the time.

In the master, the SPE, MSTR, and CPHA-bits of SPICR1 are set. SPICR0 is 0. I set the SPTIE and SPIE- bits right after the first byte is transmitted.

In the slave, the SPIE, SPE, MSTR, and CPHA-bits are set. SPICR0 is 0.

I also found that the slave data does not clock its data until the third byte. Maybe there's something I have missed that causes this, but I can live with it. I use sync and key data to detect messages anyway.

Moreover, you have to make sure that both ends are initialised before transmission begins.

Good luck!