Christian Böhme wrote:
thereza wrote:
Also, with the built in frequency multiplier can I get a stable 8Mhz (or 16)
with just a watch crystal -- enough for some high speed serial communication
via the uart/spi?
The User's Guide goes into minute detail about the available clock modules and
the clock signals derived from them (SMCLK is the one you're wanting for SPI):
http://focus.ti.com/lit/ug/slau049f/slau049f.pdf
Chapter 4 has all the details while fig 4-1 gives a schematic. I fail, however,
to see a frequency _multiplier_ (other than a rational number <= 1, that is) in
that schematic ...
That's because the msp430 does not have a PLL, which is the most common
way for small microcontrollers to multiply a clock frequency.
There are other ways to achieve the effect you are looking for. I have
often connected a 32 kHz watch crystal to the auxiliary oscillator, and
used that as a basis for a timer, while running the main clock from the
internal oscillator. By sampling the 32 kHz timer based on the main
clock timer, or vice versa, you can figure out the exact frequency of
the internal oscillator. Then you either tune the internal oscillator
to the frequency you want, or modify your baud rate divider
appropriately. I have systems where the main clock might vary from 4 to
5 MHz depending on the temperature or the particular part, but
time-critical functions like the UART are better than 0.1% accuracy.
