On Mon, Jun 15, 2009 at 6:32 AM, JMGross<[email protected]> wrote: > > > > > ----- Ursprüngliche Nachricht ----- > Von: Mark Rages > Gesendet am: 11.Juni.2009 18:54:13 > >>> My own experiences with the UART programming is that the internal RC clock >>> is way too unstable and exact to produce a stable communication. >>> With 4MHz RC clock I was unable to establish a reliable link with 9600 >>> Baud, while with the same code and an external 8 MHz quarts even a baudrate >>> of 115KBaud was no problem. >>> At least you'll need an external 32KHz clock-quartz and some timer-driven >>> code to build something like a software-PLL to keep the RC oscillator in >>> the proper range. > >>Were you using the calibrated clock? >>"Internal Frequencies up to 16 MHz With Four Calibrated Frequencies to<1% " >><- from msp430f22x2 datasheet. >>Later on in the datasheet it claims <2.5% over frequency, still close >>enough for reliable async comms. >>If the frequency is off, it's off -- the baudrate makes no difference. > > Won't help on the 1611, as it has no calibrated clock source :) > Also, even the calibrated source won't help if the device has a large > operating temperature range. > If it has to operate in industrial environment with -25 to 85 degree celsius > (or even just 0..70) the temperature drift is likely way too much for a > stable communication. So you still have to measure temp and adjust the > divisor constantly. > > The 1% is for one of the four given frequencies, the 2.5% over the whole > frequency range, but all just for a given temperature. > I don't have one of the 2xxx datasheets as we don't use it, but what does it > say about temperature drift? >
2.5% is over temperature (0..85C). I made a mistake when I wrote 'frequency' above. It also varies with voltage a little bit -- looks like it's calibrated at 3V. Still, stable enough for async comms. I would guess that the oscillator is similarly stable at other frequencies, but the datasheet doesn't guarantee it. The calibration is just a value factory-stored in segment A memory that you can read and program into BCSCTL1 and DCOCTL. Regards, Mark markra...@gmail -- Mark Rages, Engineer Midwest Telecine LLC [email protected]
