The external resistor will help reducing the temperature and voltage
dependency of DCO frequency. However, I think there is still about
15% variation from chip to chip.
Do you have a 32kHz crystal or something else as a reference for
calibration?
Another way is to use the incoming serial data as a reference. But
you need the cooperation of the device that is sending serial data.
The Boot-Strap Loader uses such a scheme. I used the same
scheme and implemented auto-baud detect as well. It works well
for 9.6 to 115.2 kb/s. But I was not using an USART. I was doing
bit-banging and it was half-duplex only.
"Rasche, Greg" <greg.ras...@windriver.com> wrote:
I need to generate an accurate CPU clock using the internal MSP430F169
DCO. The 800K default SMCLK is very temperature sensitive, and does a bad job
generating the BAUD UART CLK. I want 115,200 baud, and the DCO and internal
resistors generate bad UART rates.
I can install a 0.1% external resistor if I need it. It seems like there
would be a table in the MSP PDF files that says that with 3.3V you need
external resistor value X to generate Y MHz. I can not find that table.
I know that "controlling the DCO frequency of the MSP430x11x" SLAA047
exists. There must be an easier way the get an accurate 115,200 baud rate with
the DCO.
Is there an easy way to get SMCLK to run at 4 MHz or 8 MHz?
greg
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