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SPI Timer2 CLK doesn't work if SPI_H_TO_L is set

 
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Thorsten
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SPI Timer2 CLK doesn't work if SPI_H_TO_L is set
PostPosted: Sat Feb 28, 2009 12:40 pm     Reply with quote
Hi,

I'm using a PIC18F24J10 and i need a max. 70kHz SPI Clock. The PIC have a 10MHZ ocsillator. So I decide to use the Timer2 as SPI Clock source. But that works only if the SPI is set to SPI_L_TO_H but not on SPI_H_TO_L. I am using 4.057.

Could anyone help me on my problem?

Thorsten
PCM programmer



Joined: 06 Sep 2003
Posts: 21708

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PostPosted: Sat Feb 28, 2009 4:54 pm     Reply with quote
What chip are you using as the SPI slave ? Normally, the data sheet
for the slave chip will specify the required SPI mode. The SPI mode will
be one of these four modes:
Code:
// SPI modes
#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)

Normally we prefer to use these constants for the SPI mode, instead
of using "SPI_L_TO_H", etc., because it's easier.

Post a link to the web page for the SPI slave chip.


There is an errata on using Timer2 as the source for the SPI clock
for some PICs. I don't see this bug listed on the errata sheet for
the 18F24J10, but it still could be present (but not admitted yet by
Microchip).
Thorsten
Guest
PostPosted: Sun Mar 01, 2009 1:08 am     Reply with quote
Hi,

i´m using a QT1106 Wheel IC. Please google for the Datasheet because i can´t post the link (GUEST Acount ) The SPI Mode must be Mode 3. Any more suggestions?

Thanks fpor help.

Thorsten
PCM programmer



Joined: 06 Sep 2003
Posts: 21708

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PostPosted: Sun Mar 01, 2009 1:51 am     Reply with quote
Here's the link to the web page.
http://www.qprox.com/products/Page-16067/qt1106.html

SCLK idles high and it samples on the rising edge. That's SPI mode 3:
http://www.totalphase.com/support/kb/10045/#modes
Are you using the following configuration for your setup_spi() statement ?
Code:
#define SPI_MODE_3  (SPI_H_TO_L | SPI_XMIT_L_TO_H)
Thorsten
Guest
PostPosted: Sun Mar 01, 2009 2:02 am     Reply with quote
Yes, i use this setting. I just tried it on a PIC18F87J10 with the same result.
I will try it now on a PIC16. I will inform you about the result.
Anymore Hints?

Greetings

Thorsten
Thorsten
Guest
PostPosted: Sun Mar 01, 2009 2:21 am     Reply with quote
On a PIC18F452 it works.
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