Josh Koffman <joshybear <at> gmail.com> writes:

Hello Josh,
> 
> Alright, I've been reading the datasheet and now I have more questions
> (go figure)!
> 
> I've been looking at DS39631A - the PIC18F2520 datasheet.
> 
> On page 166 (section 17.3.5 Master Mode) it's talking about the SPI
> clock rate and how we can select it. The following options are given:
> 
> Fosc/4 (or Tcy)
> Fosc/16 (or 4 . Tcy)
> Fosc/64 (or 16 . Tcy)
> Timer2 Output/2
> 
> So my question is...should the dot that preceeds the Tcy be something
> else? If it really does mean multiplied by, I just don't understand
> it...Fosc/16 should be 1/4 the instruction speed correct?

It takes 4 clock cycles for one instruction, therefore Tcy = 1/(Fosc/4).
One way to think about it is that "frequency" of instructions is Fosc/4.  
For MSSP clock speed Fosc/16 you will have Fmssp = Fosc/16, while period of the 
clock Tmssp = 4*Tcy.  


> 
> Second, am I correct in determining that if I want to clock data out
> of my wireless module, I should keep my PIC in master mode so that it
> generates the clock signal? If so, from my understanding I need to
> write a byte to the SSPBUF register. At that point my data will be
> clocked out as the incominging data is clocked back into SSPBUF.
> 

I did not use MSSP in SPI mode, but in I2C the module will first clock out 
address and indicate read/write mode (last bit of the address).  Slave will 
provide data if master requests a read.  The master provides the clock.

<SNIP>

Sergey Dryga
Beaglerobotics.com

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