What is the SPI SCK Clock Output?

Hi,

I want to know what is the clock speed of the Arduino Duemilanove for the SCK pin used for SPI; it is the same frequency of 16 Mhz?

It is changeable. Default speed may be 4 MHz.
Whatever it is, it is pretty quick. Works well for sending data to MAX7221, TPIC6B595 shift registers, DACs.

This speeds it up a lot

SPI.setClockDivider( SPI_CLOCK_DIV2 );

You can see some screen shots of the difference in this thread
http://arduino.cc/forum/index.php/topic,100667.0.html
(Thanks again Nick!)

I am using the SC16IS750 which is a SPI to UART converter. The problem is that in Arduino is working, but I need it to work in dsPIC33FJ. I translated the code almost as similar as possible as I can. The problem is that I am receiving values like: ÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀ, or ÿÿÿÿÿÿÿÿÿÿ is I change the baudrate, when using dsPIC33FJ but using Arduino it gives me the correct string.

Any idea of why this can be happening?