Hi there.

I'm using a MSP430F149 in my graduation project and
I'd like to ask some questions about the UART and
clock generation.

The project and the problem:

I'm trying to develop an IrDA compliant communication
board using the MSP uC.
I'm using the TI IrDA Encoder/Decoder TIR1000 and a
Vishay Telefunken TFDU4100 transceiver. The TIR1000 is
connected to the MSP UART1. Transmission is OK but
reception is buggy. I believe the cause is lack of
synchronism between the UART and the TIR1000 because
the TIR needs a input clock signal 16x the baud rate
(pin 16XCLK). How can I generate this clock signal?

My Clock configuration:

I have a 8Mhz crystal and a 32768 Hz watch crystal and
my clock configuration follows:
	// MCLK is 8 MHz (from XT2)
	// SMCLK is 8 MHz (from XT2)
	// ACLK is 32 kHz (from XT1)
I don't use SMCLK and ACLK to anything so I can change
the clock source to any other configuration.

My UART configuration:

I just want a 9600 connection. Here is my code for
UART config (in C):

// No parity, one stop bit, 8 bit data length, UART
mode
    U1CTL = CHAR;
    U1TCTL = SSEL1;  // UCLK = SMCLK
    U1BR0 = 0x41;    // 8Mhz / 9600 = ~833.33 = 0341h
    U1BR1 = 0x03;
    UMCTL1 = 0x21;   // Modulation .33 = 21h
    ME2 |= UTXE1 + URXE1; // Enable USART1 TXD/RXD
    IE2 |= UTXIE1 + URXIE1; // Enable USART1 TX/RX
interrupt

The Question:

For a 9600 speed the 16XCLK pin should receive a
153.6kHz clock signal.
I tried to use Timer_A P1.2/TA1 but no good. Here's
the question: Is there a way to use the SMCLK (8MHz)
to generate a exact 153.6kHz clock? If no, can I
source the SMCLK from the DCO, calibrate it to 153.6k
and put it through pin P1.2? If yes, how (I'm not
familiar with DCO)? Can someone share some C code that
does the trick?

Any other suggestions?

Note: I'm using a 3.6V suply so the clock system is
really running at ~8MHz.

Any help will be greatly apreciated.

Thanks for your attention,
Eduardo Zambon.

______________________________________________________________________

Hi Eduardo

Keep in mind that the DCO can vary in frequency with changing 
temperatures. If you want to eliminate that, use an external Rosc. A 
100K value to Vcc will make the default value about 2MHz (plus or 
minus a couple percent), and it won't be temperature dependent. You 
can adjust from there to get your 8 Mhz. 

You can calibrate the 8MHz by using the 32KHz clock. You just count 
the number of SMCLK pulses inside one or more 32KHz periods and 
adjust the DCO bits accordingly. Since you're using an external 
Rosc, you only need to do this at power-up, and can reuse the timers 
for other functions.

For your external 153.6 clock, you can take your 8MHz into one of 
the timers (via SMCLK) and divide it, and put it out on one of the 
timer outputs. For example, if you have 8 mHz going into TimerA, 
then set one of the timer channels to count to 8,000,000/153,600/2 26. Everytime
you get a interrupt, you flip the signal and add 26 so 
that it looks for the next interrupt. Since it's not an exact 
multiple of 8MHz, you have to handle the rollover also. Or if you 
have a completely empty timer, just have it roll over at 26 and use 
that.

Good job setting Vcc to 3.6V. Many users overlook that. TI will also 
be releasing an IrDA appnote in the next couple of months with a 
full IrDA stack. I think it's being written for the 'F169. Might be 
a little late for you though... Send me an e-mail offline and we can 
discuss. 

Mike.

--- In msp430@msp4..., Eduardo Zambon <zambon_e@y...> wrote:
> Hi there.
> 
> I'm using a MSP430F149 in my graduation project and
> I'd like to ask some questions about the UART and
> clock generation.
> 
> The project and the problem:
> 
> I'm trying to develop an IrDA compliant communication
> board using the MSP uC.
> I'm using the TI IrDA Encoder/Decoder TIR1000 and a
> Vishay Telefunken TFDU4100 transceiver. The TIR1000 is
> connected to the MSP UART1. Transmission is OK but
> reception is buggy. I believe the cause is lack of
> synchronism between the UART and the TIR1000 because
> the TIR needs a input clock signal 16x the baud rate
> (pin 16XCLK). How can I generate this clock signal?
> 
> My Clock configuration:
> 
> I have a 8Mhz crystal and a 32768 Hz watch crystal and
> my clock configuration follows:
> 	// MCLK is 8 MHz (from XT2)
> 	// SMCLK is 8 MHz (from XT2)
> 	// ACLK is 32 kHz (from XT1)
> I don't use SMCLK and ACLK to anything so I can change
> the clock source to any other configuration.
> 
> My UART configuration:
> 
> I just want a 9600 connection. Here is my code for
> UART config (in C):
> 
> // No parity, one stop bit, 8 bit data length, UART
> mode
>     U1CTL = CHAR;
>     U1TCTL = SSEL1;  // UCLK = SMCLK
>     U1BR0 = 0x41;    // 8Mhz / 9600 = ~833.33 = 0341h
>     U1BR1 = 0x03;
>     UMCTL1 = 0x21;   // Modulation .33 = 21h
>     ME2 |= UTXE1 + URXE1; // Enable USART1 TXD/RXD
>     IE2 |= UTXIE1 + URXIE1; // Enable USART1 TX/RX
> interrupt
> 
> The Question:
> 
> For a 9600 speed the 16XCLK pin should receive a
> 153.6kHz clock signal.
> I tried to use Timer_A P1.2/TA1 but no good. Here's
> the question: Is there a way to use the SMCLK (8MHz)
> to generate a exact 153.6kHz clock? If no, can I
> source the SMCLK from the DCO, calibrate it to 153.6k
> and put it through pin P1.2? If yes, how (I'm not
> familiar with DCO)? Can someone share some C code that
> does the trick?
> 
> Any other suggestions?
> 
> Note: I'm using a 3.6V suply so the clock system is
> really running at ~8MHz.
> 
> Any help will be greatly apreciated.
> 
> Thanks for your attention,
> Eduardo Zambon.
> 
> 
_____________________________________________________________________
_
> 
>