Hi Chris, The fll_adjust() function from the mspgcc library works perfect. The UART works as desired at 115,200. I added a 100K external resistor, and set the fll_adjust() desired clock rate to 7 MHz. I chose 7 MHz because of this comment in the "[Mspgcc-users] msp430 CPU clock" email thread on 8/19/2006.
-> Be aware, that maximum CPU clock is supply -> voltage dependant! Check -> http://focus.ti.com/lit/ds/symlink/msp430f148.pdf page 24. -> For 3.3V max is at about 7.2MHz. I do not really need to run at 7 MHz. I could run at 4M or slightly slower, if needed. Questions: 1) What are CPU frequency ranges available, if I use the 270K ROSC (rather than the 100K) as you suggest below? Where is that table? 2) do I need to re-run fll_adjust() from time-to-time as the device changes temperature? Thanks for the help! Greg -----Original Message----- From: mspgcc-users-boun...@lists.sourceforge.net [mailto:mspgcc-users-boun...@lists.sourceforge.net] On Behalf Of Chris Liechti Sent: Friday, August 25, 2006 6:22 PM To: GCC for MSP430 - http://mspgcc.sf.net Subject: Re: [Mspgcc-users] MSP430F169 DCO for UART clock Lichen Wang schrieb: > The method in slaa047.pdf is trying to adjust the DCO to maintain a > certain desired frequency. I do not think you need to do that. What > you need is to get a high enough DCO frequency and to know what that frequency is. > > I suggest the following: > > (a) Add an external resistor (100K, 1%) and set Rosc=1 a value around 270k will give better stablity over temperature but no so high frequencies > (b) Set RSELx=7 (instead of default =4), default DCO+MOD are fine (The > above should give you stable and fast enough DCO frequency.) > (c) Use the 32768Hz to generate a 4096Hz ACLK. (32768 / 8=4096) > (d) Use the DCO output as MCLK and SMCLK. > (e) Use TimerA or TimerB, clock it with SMCLK and use the capture mode > to capture the rising (or falling) edge of ACLK. > (f) The difference of consecutive captured counts times 4096 is the > frequency of SMCLK. > (g) Use this measure frequency of SMCLK to set the baudrate divider. > (h) You can free (or stop) the 32768Hz and the Timer for other use. you can use the fll_adjust() function from the mspgcc library. it implements this. there is an example in "examples/libraries" [...] > 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. that's without calibration. once that is done, you can save the clock settings in the flash. however you'still only have +/-5% which isn't accurate enough for the serial port (not over the entire temperaure range at least). (the msp430-dco tool can be used to get calibration values, parallel port JTAG only) chris ------------------------------------------------------------------------ - Using Tomcat but need to do more? Need to support web services, security? Get stuff done quickly with pre-integrated technology to make your job easier Download IBM WebSphere Application Server v.1.0.1 based on Apache Geronimo http://sel.as-us.falkag.net/sel?cmd=lnk&kid=120709&bid=263057&dat=121642 _______________________________________________ Mspgcc-users mailing list Mspgcc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/mspgcc-users
