关于MSP430G2412 的CCIxB问题

您好：

    看MSP430G2412官方例程的时候，关于定时器TACCTL0寄存器配置的时候，CCISx  Capture/compare input select 设置成了01 CCIxB。可是我对应MSP430G2412的引脚看的时候，好像没有CCIxB的引脚。能解释下为什么吗？    谢谢。

官方例程是

//******************************************************************************
// MSP430G2xx2 Demo - Timer_A, Ultra-Low Pwr UART 2400 Echo, 32kHz ACLK
//
// Description: Use Timer_A CCR0 hardware output modes and SCCI data latch
// to implement UART function @ 2400 baud. Software does not directly read and
// write to RX and TX pins, instead proper use of output modes and SCCI data
// latch are demonstrated. Use of these hardware features eliminates ISR
// latency effects as hardware insures that output and input bit latching and
// timing are perfectly synchronised with Timer_A regardless of other
// software activity. In the Mainloop the UART function readies the UART to
// receive one character and waits in LPM3 with all activity interrupt driven.
// After a character has been received, the UART receive function forces exit
// from LPM3 in the Mainloop which echo's back the received character.
// ACLK = TACLK = LFXT1 = 32768Hz, MCLK = SMCLK = default DCO
// //* An external watch crystal is required on XIN XOUT for ACLK *//
//
// MSP430G2xx2
// -----------------
// /|\| XIN|-
// | | | 32kHz
// --|RST XOUT|-
// | |
// | CCI0B/TXD/P1.5|-------->
// | | 2400 8N1
// | CCI0A/RXD/P1.1|<--------
//
#define RXD 0x02 // RXD on P1.1
#define TXD 0x20 // TXD on P1.5

// Conditions for 2400 Baud SW UART, ACLK = 32768

#define Bitime_5 0x06 // ~ 0.5 bit length + small adjustment
#define Bitime 0x0E // 427us bit length ~ 2341 baud

unsigned int RXTXData;
unsigned char BitCnt;

void TX_Byte (void);
void RX_Ready (void);

// D. Dang
// Texas Instruments Inc.
// December 2010
// Built with CCS Version 4.2.0 and IAR Embedded Workbench Version: 5.10
//******************************************************************************

#include <msp430g2452.h>

void main (void)
{
WDTCTL = WDTPW + WDTHOLD; // Stop watchdog timer
CCTL0 = OUT; // TXD Idle as Mark
TACTL = TASSEL_1 + MC_2; // ACLK, continuous mode
P1SEL = TXD + RXD; //
P1DIR = TXD; //

// Mainloop
for (;;)
{
RX_Ready(); // UART ready to RX one Byte
_BIS_SR(LPM3_bits + GIE); // Enter LPM3 w/ interr until char RXed
TX_Byte(); // TX Back RXed Byte Received
}
}

// Function Transmits Character from RXTXData Buffer
void TX_Byte (void)
{
BitCnt = 0xA; // Load Bit counter, 8data + ST/SP
while (CCR0 != TAR) // Prevent async capture
CCR0 = TAR; // Current state of TA counter
CCR0 += Bitime; // Some time till first bit
RXTXData |= 0x100; // Add mark stop bit to RXTXData
RXTXData = RXTXData << 1; // Add space start bit
CCTL0 = CCIS0 + OUTMOD0 + CCIE; // TXD = mark = idle
while ( CCTL0 & CCIE ); // Wait for TX completion
}

// Function Readies UART to Receive Character into RXTXData Buffer
void RX_Ready (void)
{
BitCnt = 0x8; // Load Bit counter
CCTL0 = SCS + OUTMOD0 + CM1 + CAP + CCIE; // Sync, Neg Edge, Cap
}

// Timer A0 interrupt service routine
#pragma vector=TIMER0_A0_VECTOR
__interrupt void Timer_A (void)
{
CCR0 += Bitime; // Add Offset to CCR0

// TX
if (CCTL0 & CCIS0) // TX on CCI0B?
{
if ( BitCnt == 0)
CCTL0 &= ~ CCIE; // All bits TXed, disable interrupt
else
{
CCTL0 |= OUTMOD2; // TX Space
if (RXTXData & 0x01)
CCTL0 &= ~ OUTMOD2; // TX Mark
RXTXData = RXTXData >> 1;
BitCnt --;
}
}
// RX
else
{
if( CCTL0 & CAP ) // Capture mode = start bit edge
{
CCTL0 &= ~ CAP; // Switch from capture to compare mode
CCR0 += Bitime_5;
}
else
{
RXTXData = RXTXData >> 1;
if (CCTL0 & SCCI) // Get bit waiting in receive latch
RXTXData |= 0x80;
BitCnt --; // All bits RXed?
if ( BitCnt == 0)
//>>>>>>>>>> Decode of Received Byte Here <<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<
{
CCTL0 &= ~ CCIE; // All bits RXed, disable interrupt
_BIC_SR_IRQ(LPM3_bits); // Clear LPM3 bits from 0(SR)
}
//>>>>>>>>>> Decode of Received Byte Here <<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<
}
}
}