MSP430FR5739: UART not working when running at other Clock Frequencies when using recommended register values

Thanks for your response Clemens.  I tried the values as suggested and it works for 8MHz Clock producing 9600 baud.  According to table 18-5, the same values can be used for a 16MHz clock to produce 19200 baud, however, it does not produce a valid result.  For the register entries I am using the following:

CSCTL1 |= DCOFSEL_0 + DCORSEL;             // Set Clock to 16MHz

UCA0BRW = 52;
UCA0MCTLW = UCBRF_1 + (0x49 * UCBRS0) + UCOS16;

Is this the correct way to populate these registers for 16MHz clock and 19200 baud?  If not, please advise.

I really appreciate your input since to me it is very confusing and I am really needing to get UART working.  I don't care what baud - but any baud at 16MHz.  Any example working code for this would be helpful.

Thanks

CSCTL1 |= DCOFSEL_0 + DCORSEL;             // Set Clock to 16MHz

This actually sets the clock to 24 MHz. (By default, both FSEL bits are set; and "|=" does not clear any bits.)

I do not know where table18-5 got those values from. The USCI UART Calculator says BRW = 26, MCTLW = UCOS16 + UCBRF_1 + 0 * UCBRS0 in oversampling mode, but that results in higher errors than without oversampling, so you should instead use BRW = 416, MCTLW = UCBRF_0 + 6 * UCBRS0.

Hi Clemens,

Thanks again for your reply.  I tried both sets of numbers and they both do not work.  I also tried other values from the UART calculator (thanks for the link), and they do not work either.  Example of what I tried using the values you suggested - with a 16MHz clock:

UCA0BRW = 416;
UCA0MCTLW = UCBRF_0 + 6 * UCBRS0;
UCA0CTLW0 |= UCSWRST + UCMODE_0 + UCSSEL_2;

Would there be something else that would cause this to not work?  Surely the online calculator should give valid values.  Could you please send me the code that would work?

Thanks

Hi Clemens,

I looked at each of the 3 *CS.c files for the MSP430FR57xx and none of them use an external crystal.  So, I will ignore the External Crystal and focus on getting the internal crystal working - using the clock settings I mentioned above.  When I set up UART as per the values you gave me, I do get a response on the terminal and it looks like this:

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Coul.d you please advise if there is anything else I can try to get this working?  Would you have an example of code that uses 16MHz Crystal and 38400 (or any other baud except 9600)?

Thanks

There is no internal crystal. The DCO/VLO are not crystals but R/C oscillators; this is why they are not very accurate.
According to the datasheet, the DCO frequency trimmed for "16 MHz" typically runs at 16.2 MHz, and has errors up to 20000 ppm at normal temperatures.

If possible, you should derive the UART clock from a crystal. CS_03.c shows how to start up an external crystal on XT1 in low-frequency mode. (What crystal do you have?)

Alternatively, try to compute the baud rate registers for a base clock of 16.2 MHz (or measure what the frequency actually is on your chip).

You get such garbage when the clocks of the sender and the receiver don't match.
What is the actual ACLK frequency? (Configure P2.0 to output ACLK, and measure that.)

In theory, this does not look like erratum USCI44. But to be safe, configure both ACLK and MCLK to be sourced from XT1.

I have set MCLK to = ACLK as per the following code.  This code works for the 9600 baud, but no other baud rate.

GPIO_setAsPeripheralModuleFunctionInputPin(GPIO_PORT_PJ,GPIO_PIN4 + GPIO_PIN5,
GPIO_PRIMARY_MODULE_FUNCTION
);

CS_setDCOFreq(DCORSEL,DCOFSEL_2);                                                                        // Set DCO Frequency to 16MHz
CS_initClockSignal(CS_ACLK,CS_XT1CLK_SELECT,CS_CLOCK_DIVIDER_1);                 // Initialise ACLK=XT1 and CLK DIVIDER to 1
CS_initClockSignal(CS_SMCLK,CS_XT1CLK_SELECT,CS_CLOCK_DIVIDER_1);              // Initialise SMCLK=DCOCLK and CLK DIVIDER to 2
CS_initClockSignal(CS_MCLK,CS_XT1CLK_SELECT,CS_CLOCK_DIVIDER_1);                // Initialise MCLK=DCOCLK and CLK DIVIDER set to 1
CS_setExternalClockSource(16000000,0);                             // Set XT1 frequency
CS_turnOnXT1(CS_XT1_DRIVE_0);                                     // Start XT1 external crystal

I have also configured P2.0 to output the ACLK signal and it is reading 15.997MHz, so ACLK seems to be running ok.

Any other suggestions?

In both cases, the measured frequency is off by about 1.3 %. It's likely that this prevents correct reception at higher baud rates.

Please try without oversampling.

If you want to ensure that the UART works at high baud rates, use a baud rate crystal (e.g., 14.7456 MHz) instead.

Hi Clemens,

So far I have tried all your suggestions - apart from the external 14.7456MHz crytal - and none of them has worked. I have also tried the external 16.0000MHz crystal - and that did not make a difference either. 
Conclusion: The MSP-EXP430FR5739 Dev board only works at 8MHz clock, 9600 baud or 16MHz clock, 9600 baud - with or without an external crystal. All the UART example code from TI is for 9600 baud only. Also, I am able to get other baud rates working on a lesser MCU (MSP430FR2311) - using the same determined register values for UCAxxx.

Could TI please provide code that works at a different baud rate than 9600, or am I to conclude that the MSP430FR57xx series / or the Launchpad does not support other baud rates?

Please advise.

Thanks

Hi, Timothy, I do not mean it is a hardware issue, I just suggested you check the system step by step.If the system does not work as you expected, It is caused either by soferware or hardware. The USART is an asynchronous communication, It is also determined by the accuracy of the oscillator, so I suggested you short the TX pin and RX pin, to see whether you can receive a right value and to chek the waveform.