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问 最近准备做一个串行通信的 程序
就是将AD（单通道）每次转换的结果再转换完成后直接通过串口传入电脑，在传入的过程中AD还要继续进行AD转换，不间断的转换和传输，直到发指令结束（通过PC程序的主界面）。打算采用F149
有这样几个问题：
（1）看到在串口电平转换的时候，有的用美信232有的用3221还有3223，有什么区别，怎么选用
（2）在AD转换的过程我是应当采用单通道单次转换不断循环的方式还是什么？
（3）我的信号频率大概在2K左右，这样为了保证实时性和信号的不遗漏的传输，我应该选择的波特率大概多少？打算选用32K的晶振。
（4）看了一个例子，有些启发，不知道怎么改成合适的，还请高人出手帮我看看，感谢
//**************************************************************************
//*
//* ADC12 Test Program for MSP430F149 HeCh, 26.05.00
//*
//* This demo program shows the use of sequence measurement triggered
//* by one single signal. Mutliple Sample&Hold feature is used here.
//* No interrupts are used!!
//* One single conversion sequence is initiated. The sequence is
//* triggered by software using the ADC12SC bit. After the sequence
//* is finished the results are transmitted via RS232 (USART module of
//* MSP430 is used). After that the next conversion sequence is initiated.
//*
//* All 16 ADC12MEMx Registers are used by this program:
//* ADC12MEM0 contains the input A0 conversion result,
//* ADC12MEM1 contains the input A1 conversion result, and so on.
//*
//* The conversion results are transmitted via the USART module (using
//* TXD Pin P3.6).
//* USART Settings: 4800 baud, 8 data bits, even parity, 1 stop bit
//*
//**************************************************************************

#include "MSP430x149x.h" // Standard Definition Control Register
#define ADCMEM ((int*) 0x0140) // ADC12MEMx definition
//--------------------------------------------------------------------------
void Init(void); // Initialization of System/Control Registers
void SendResult(void); // conversion result is sent via RS232
int Digit0(int Register); // LSB nibble (digit 0) of Register is sent back
int Digit1(int Register); // middle nibble (digit 1) of Register is sent back
int Digit2(int Register); // MSB nibble (digit 2) of Register is sent back
int Hex2ASCII(int hex); // conversion of hexadecimal number into ASCII
//--------------------------------------------------------------------------

void main(void)
{ unsigned int i;

Init(); // Initialization

while (1)
{
ADC12CTL0 |= 0x01; // start sampling (trigger signal for one sequence)

while ((ADC12CTL1&0x01)==1); // wait until AD conversion of the
// whole sequence is finished

SendResult(); // send conversion results via RS232
for (i=0;i<=40000;i++); // wait loop (delay between sequences)
}
}


void Init(void)
{ WDTCTL = WDTPW + WDTHOLD; // Stop watchdog timer

/* USART Settings:
UART function, Idle line multiprocessor Protocol,
4800 baud, 8 data bits, even parity, 1 stop bit */
UCTL1 &=~ SWRST; // reset SWRST bit
UCTL1 = 0xD0;
UBR01 = 0x06;
UBR11 = 0x00;
UMCTL1 = 0x6F;
UTCTL1 = 0x10;
URCTL1 = 0x00;
ME2 |= 0x20; // enable USART transmit

P3SEL = 0x40; // Pin P3.6 used by USART module
P3DIR = 0x40; // Pin P3.6 is output

/* ADC12 Settings: */
P6SEL = 0xFF; // Pin P6 used by ADC module

ADC12CTL0 &=~ 0x02; // Disable conversion before changing
// the ADC12 settings!!!
/* selection of reference and input */
ADC12MCTL0 = 0x00; // Ref = AVss, AVcc; Input = A0
ADC12MCTL1 = 0x01; // Ref = AVss, AVcc; Input = A1
ADC12MCTL2 = 0x02; // Ref = AVss, AVcc; Input = A2
ADC12MCTL3 = 0x03; // Ref = AVss, AVcc; Input = A3
ADC12MCTL4 = 0x04; // Ref = AVss, AVcc; Input = A4
ADC12MCTL5 = 0x05; // Ref = AVss, AVcc; Input = A5
ADC12MCTL6 = 0x06; // Ref = AVss, AVcc; Input = A6
ADC12MCTL7 = 0x07; // Ref = AVss, AVcc; Input = A7
ADC12MCTL8 = 0x08; // Ref = AVss, AVcc; Input = A8
ADC12MCTL9 = 0x09; // Ref = AVss, AVcc; Input = A11
ADC12MCTL12 = 0x0C; // Ref = AVss, AVcc; Input = A9
ADC12MCTL10 = 0x0A; // Ref = AVss, AVcc; Input = A10
ADC12MCTL11 = 0x0B; // Ref = AVss, AVcc; Input = A12
ADC12MCTL13 = 0x0D; // Ref = AVss, AVcc; Input = A13
ADC12MCTL14 = 0x0E; // Ref = AVss, AVcc; Input = A14
ADC12MCTL15 = 0x8F; // Ref = AVss, AVcc; Input = A15
// ADC12MCTL15 is end of sequence
// (EOS bit is set!)

ADC12CTL1 = 0x0202; // first conv. result is stored in ADC12MEM0
// ADC12SC bit triggers Sample&Hold
// sample pulse is generated by Sampling Timer
// Clock Source: ADC12 internal oscillator
// Clock divider: 1
// conversion mode: one single sequence

ADC12CTL0 = 0x0090; // Sample&Hold Time 0
// Sample&Hold Time 1
// Multiple Sample&Hold
// reference voltage is off
// ADC12 module is switched on
// no interrupts

ADC12CTL0 |= 0x02; // enable conversion
}


void SendResult(void)
{ char prompt1[81]="\r---------------------------------------\r\
mem0 mem1 mem2 mem3 mem4 mem5 mem6 mem7\r";
char prompt2[42]="\r\rmem8 mem9 memA memB memC memD memE memF\r";
int i;


for (i=0;i<=80;i++) // transmit " MEM" via RS232
{ TXBUF1=prompt1[i];
while ((UTCTL1&0x01)==0);
}

for (i=0;i<=7;i++)
{ TXBUF1='0'; // transmit "0"
while ((UTCTL1&0x01)==0);
TXBUF1=Digit2(ADCMEM[i]); // transmit digit 2 of ADC12MEMx
while ((UTCTL1&0x01)==0);
TXBUF1=Digit1(ADCMEM[i]); // transmit digit 1 of ADC12MEMx
while ((UTCTL1&0x01)==0);
TXBUF1=Digit0(ADCMEM[i]); // transmit digit 0 of ADC12MEMx
while ((UTCTL1&0x01)==0);
TXBUF1=' '; // transmit " "
while ((UTCTL1&0x01)==0);
}

for (i=0;i<=41;i++) // transmit " MEM" via RS232
{ TXBUF1=prompt2[i];
while ((UTCTL1&0x01)==0);
}

for (i=8;i<=15;i++)
{ TXBUF1='0'; // transmit "0"
while ((UTCTL1&0x01)==0);
TXBUF1=Digit2(ADCMEM[i]); // transmit digit 2 of ADC12MEMx
while ((UTCTL1&0x01)==0);
TXBUF1=Digit1(ADCMEM[i]); // transmit digit 1 of ADC12MEMx
while ((UTCTL1&0x01)==0);
TXBUF1=Digit0(ADCMEM[i]); // transmit digit 0 of ADC12MEMx
while ((UTCTL1&0x01)==0);
TXBUF1=' '; // transmit " "
while ((UTCTL1&0x01)==0);
}

TXBUF1=13; // send carriage return
while ((UTCTL1&0x01)==0);
}

int Digit0(int Register) // return LSB nibble (digit 0)
{ int result;

result = Hex2ASCII(0x0F & Register);
return result;
}

int Digit1(int Register) // return nibble (digit 1)
{ int result;

result = Register >> 4;
result = Hex2ASCII(0x0F & result);
return result;
}

int Digit2(int Register) // return MSB nibble (digit 2)
{ int result;

result = Register >> 8;
result = Hex2ASCII(0x0F & result);
return result;
}

int Hex2ASCII(int hex) // hexadecimal to ASCII conversion
{ int result;

if (hex<=9)
{ result=hex+'0'; } // convert number
else
{ result=hex+('A'-10); } // convert letter

return result;

}