利用1121仿波特率为9600串口遇到的怪现象

huangnian 2006-6-8 17:23 楼主

我根据TI代码改写的程序：下面是TI的例子
;******************************************************************************
; MSP430x11x1 Demo - Timer_A, Ultra-Low Pwr UART 9600 Echo, 32kHz ACLK
;
; Description: Use Timer_A CCR0 hardware output modes and SCCI data latch to
; to implement UART function @ 9600 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.
;
; To demonstrate 9600 buad with a 32768 XTAL used as the buad rate generator,
; a look-up ta××e is used to modulate between a clock divider or 3 and 4.
; Using modulation, a buad rate of ~9600 is achieved.
; ACLK = TACLK = LFXT1 = 32768Hz, MCLK = SMCLK = default DCO ~800kHz
; //* An external watch crystal is required on XIN XOUT for ACLK *//
;
; MSP430F1121
; -----------------
; /|\| XIN|-
; | | | 32kHz
; --|RST XOUT|-
; | |
; | CCI0A/TXD/P1.1|-------->out0 output
; | | 9600 8N1
; | CCI0B/RXD/P2.2|<--------cci0b input
;
RXD EQU 004h ; RXD on P2.2
TXD EQU 002h ; TXD on P1.1
;
; CPU Registers Used
#define RXTXData R4
#define BitCnt R5
;
; Conditions for 9600 Baud SW UART, ACLK = 32768
Bitime_5 EQU 01 ; ~0.5 bit length + small adjustment
Bitime EQU 03 ;
;
; M. Buccini
; Texas Instruments Inc.
; Feb 2005
; Built with IAR Embedded Workbench Version: 3.21A
;*****************************************************************************
#include <msp430x11x1.h>
;-----------------------------------------------------------------------------
ORG 0F000h ; Program Start
;-----------------------------------------------------------------------------
RESET mov.w #300h,SP ; Initialize Stackpointer
StopWDT mov.w #WDTPW+WDTHOLD,&WDTCTL ; Stop WDT
SetupTA mov.w #TASSEL_1+MC_2,&TACTL ; ACLK, continuous mode
SetupC0 mov.w #OUT,&CCTL0 ; TXD Idle as Mark
SetupP1_2 bis.b #TXD,&P1SEL ; P1.1/TA0 for TXD function
bis.b #TXD,&P1DIR ; TXD output on P1
bis.b #RXD,&P2SEL ; P2.2/TA0 as RXD input
;
Mainloop call #RX_Ready ; UART ready to RX one Byte
bis.w #LPM3+GIE,SR ; Enter LPM3 w/int Until Byte RXed
call #TX_Byte ; TX Back RXed Byte Received
jmp Mainloop ;
;
;-----------------------------------------------------------------------------
TX_Byte; Subroutine that will TX Byte from RXTXData Buffer
;-----------------------------------------------------------------------------
TX_1 mov.w &TAR,&CCR0 ; Current state of TA counter
cmp.w &TAR,&CCR0 ; !!Prevent async capature!!
jne TX_1 ;
add.w #Bitime,&CCR0 ; Some time till first bit
mov.w #OUTMOD2+OUTMOD0+CCIE,&CCTL0 ; TXD = Space = Start Bit
TX_Wait bit.w #CCIE,&CCTL0 ; Wait for TX completion
jnz TX_Wait ;
ret ; Return from subroutine
;
;-----------------------------------------------------------------------------
RX_Ready; Subroutine that Readies UART to RX Byte into RXTXData Buffer
;-----------------------------------------------------------------------------
mov.w #RX_Count,BitCnt ; RX_Count --> Branch Pointer
mov.w #CM1+CCIS0+SCS+CAP+OUT+CCIE,&CCTL0 ; Neg Edge, Cap., Out
ret ; Return from subroutine
;
;-----------------------------------------------------------------------------
TA0_ISR; RXTXData Buffer holds UART Data
;-----------------------------------------------------------------------------
add.w #Bitime,&CCR0 ; Bitime till next bit
br @BitCnt+ ; Branch To Routine
;
TX_Bit1 add.w #01h,&CCR0 ;
TX_Bit rra.b RXTXData ; LSB is shifted to carry
jc TX_Mark ; Jump if bit = 1
TX_Space bis.w #OUTMOD2,&CCTL0 ; TX Space
reti ;
TX_Comp bic.w #CCIE,&CCTL0 ; All Bits RX, disa××e interrupt
TX_Mark bic.w #OUTMOD2,&CCTL0 ; TX Mark
reti ;
RX_Edge bic.w #CAP,&CCTL0 ; Switch to Compare mode
add.w #Bitime_5,&CCR0 ; First Databit 1.5 Bits from edge
reti ;
RX_Bit1 add.w #01h,&CCR0 ;
RX_Bit bit.w #SCCI,&CCTL0 ; Get bit waiting in SCCI
rrc.b RXTXData ; Store received bit
reti ;
;>>>>>>>>>> Decode of Received Byte Here <<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<
RX_Comp bic.w #CCIE,&CCTL0 ; All Bits RXed, Disa××e Interrupt
mov.w #GIE,0(SP) ; Decode Byte= Active in Mainloop
reti ;
;>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>><<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<
EVEN
RX_Count DW RX_Edge ; Special for TA
DW RX_Bit ; RX First Data Bit
DW RX_Bit1 ;
DW RX_Bit ;
DW RX_Bit ;
DW RX_Bit1 ;
DW RX_Bit ;
DW RX_Bit1 ;
DW RX_Bit ;
DW RX_Comp ; RX Complete, process RX data
TX_Count DW TX_Bit ; TX First Data Bit
DW TX_Bit1 ;
DW TX_Bit ;
DW TX_Bit ;
DW TX_Bit1 ;
DW TX_Bit ;
DW TX_Bit1 ;
DW TX_Bit ;
DW TX_Mark ; TX Stop Bit= Mark
TX_End DW TX_Comp ; TX Complete and Complete
;
;-----------------------------------------------------------------------------
; Interrupt Vectors
;-----------------------------------------------------------------------------
ORG 0FFFEh ; MSP430 RESET Vector
DW RESET ;
ORG 0FFF2h ; Timer_A0 Vector
DW TA0_ISR ;
END

我对这个例子改了点，就是接受一串字符，并根据协议执行相关指令
但是：如果我利用串口调试软件一个一个的发送字符，那么接收都正确
但是我如果发送20个（或者更多或者稍微少点）字符的话，我发现单片机有时候：

1、接受的字符串比发送的字符串少接受了几个字节（少接收的字节位置位于发送的字符串中间）。而其他的字节都正确

2、有时候会错上几个字节

我想请教高手一下，是什么原因呢？或者430利用ACLK（32.768K）就不能达到9600的拨特率。
请指点