为什么我的 PIC MCU 在串口上发送垃圾而不是正确的字？

编程问答 2022-05-03

问题描述

我编写了一个简单的代码，使用 PIC18F26K22 MCU 将一些字符串发送到 pc。 此代码适用于其他一些 MCU，但在此 MCU 上，我在输出上获得连续的 0xFF ！

如果我写 TXREG2='k' 它确实有效！但是为了发送一个字符串，程序似乎卡在了 pc_write 函数上，因为 RA0 引脚没有打开关闭并且 pc 接收连续的 0xFF 并且永不结束！

我做错了什么？！

提前致谢。

这是代码（之前在项目属性中定义了 20 Mhz 频率）

  #pragma config FOSC = HSHP      // Oscillator Selection bits (HS oscillator (high power > 16 MHz))
    #pragma config PLLCFG = OFF     // 4X PLL Enable (Oscillator used directly)
    #pragma config PRICLKEN = ON    // Primary clock enable bit (Primary clock enabled)
    #pragma config FcmeN = OFF      // Fail-Safe Clock Monitor Enable bit (Fail-Safe Clock Monitor disabled)
    #pragma config IESO = OFF       // Internal/External Oscillator Switchover bit (Oscillator Switchover 

mode disabled)

// CONfig2L
#pragma config PWRTEN = OFF     // Power-up Timer Enable bit (Power up timer disabled)
#pragma config BOREN = SBORdis  // brown-out Reset Enable bits (brown-out Reset enabled in hardware only (SBOREN is disabled))
#pragma config BORV = 190       // brown Out Reset Voltage bits (VBOR set to 1.90 V nominal)

// CONfig2H
#pragma config WDTEN = OFF      // Watchdog Timer Enable bits (Watch dog timer is always disabled. SWDTEN has no effect.)
#pragma config WDTPS = 32768    // Watchdog Timer Postscale Select bits (1:32768)

// CONfig3H
#pragma config CCP2MX = PORTC1  // CCP2 MUX bit (CCP2 input/output is multiplexed with RC1)
#pragma config PBADEN = OFF     // PORTB A/D Enable bit (PORTB<5:0> pins are configured as digital I/O on Reset)
#pragma config CCP3MX = PORTB5  // P3A/CCP3 Mux bit (P3A/CCP3 input/output is multiplexed with RB5)
#pragma config HFOFST = ON      // HFINTOSC Fast Start-up (HFINTOSC output and ready status are not delayed by the oscillator stable status)
#pragma config T3CMX = PORTC0   // Timer3 Clock input mux bit (T3CKI is on RC0)
#pragma config P2BMX = PORTB5   // ECCP2 B output mux bit (P2B is on RB5)
#pragma config MCLRE = EXTMCLR  // MCLR Pin Enable bit (MCLR pin enabled,RE3 input pin disabled)

// CONfig4L
#pragma config STVREN = ON      // Stack Full/Underflow Reset Enable bit (Stack full/underflow will cause Reset)
#pragma config LVP = ON         // Single-Supply ICSP Enable bit (Single-Supply ICSP enabled if MCLRE is also 1)
#pragma config XINST = ON       // Extended Instruction Set Enable bit (Instruction set extension and Indexed Addressing mode enabled)

// CONfig5L
#pragma config CP0 = OFF        // Code Protection Block 0 (Block 0 (000800-003FFFh) not code-protected)
#pragma config CP1 = OFF        // Code Protection Block 1 (Block 1 (004000-007FFFh) not code-protected)
#pragma config CP2 = OFF        // Code Protection Block 2 (Block 2 (008000-00BFFFh) not code-protected)
#pragma config CP3 = OFF        // Code Protection Block 3 (Block 3 (00C000-00FFFFh) not code-protected)

// CONfig5H
#pragma config CPB = OFF        // Boot Block Code Protection bit (Boot block (000000-0007FFh) not code-protected)
#pragma config CPD = OFF        // Data EEPROM Code Protection bit (Data EEPROM not code-protected)

// CONfig6L
#pragma config WRT0 = OFF       // Write Protection Block 0 (Block 0 (000800-003FFFh) not write-protected)
#pragma config WRT1 = OFF       // Write Protection Block 1 (Block 1 (004000-007FFFh) not write-protected)
#pragma config WRT2 = OFF       // Write Protection Block 2 (Block 2 (008000-00BFFFh) not write-protected)
#pragma config WRT3 = OFF       // Write Protection Block 3 (Block 3 (00C000-00FFFFh) not write-protected)

// CONfig6H
#pragma config WRTC = OFF       // Configuration Register Write Protection bit (Configuration registers (300000-3000FFh) not write-protected)
#pragma config WRTB = OFF       // Boot Block Write Protection bit (Boot Block (000000-0007FFh) not write-protected)
#pragma config WRTD = OFF       // Data EEPROM Write Protection bit (Data EEPROM not write-protected)

// CONfig7L
#pragma config EBTR0 = OFF      // Table Read Protection Block 0 (Block 0 (000800-003FFFh) not protected from table reads executed in other blocks)
#pragma config EBTR1 = OFF      // Table Read Protection Block 1 (Block 1 (004000-007FFFh) not protected from table reads executed in other blocks)
#pragma config EBTR2 = OFF      // Table Read Protection Block 2 (Block 2 (008000-00BFFFh) not protected from table reads executed in other blocks)
#pragma config EBTR3 = OFF      // Table Read Protection Block 3 (Block 3 (00C000-00FFFFh) not protected from table reads executed in other blocks)

// CONfig7H
#pragma config EBTRB = OFF      // Boot Block Table Read Protection bit (Boot Block (000000-0007FFh) not protected from table reads executed in other blocks)

// #pragma config statements should precede project file includes.
// Use project enums instead of #define for ON and OFF.
#include <xc.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h> 


void delay(int x){
 int b=0;   
    for(b=0; b<x;b++){
        
      __delay_ms(1);  
        
    }
}
    

   void pc_write(const char *data) 
{ 
   while(*data){ 
      while (TXSTA2bits.TRMT==0);
       TXREG2=(*data++); 
     }
}


int main() {
   
ANSELA=0;
ANSELB=0;
ANSELC=0;
TRISC=0b11000000;
TRISB=0b11000000; 
TRISA=0X0;
LATA=0;
LATB=0;
LATC=0;
TXSTA1bits.TXEN=1;
TXSTA1bits.SYNC=0;
RCSTA1bits.SPEN=1;
TXSTA2bits.TXEN=1;
TXSTA2bits.SYNC=0;
RCSTA2bits.SPEN=1;
RCSTA1bits.CREN=1;
RCSTA2bits.CREN=1;

TXSTA2bits.BRGH=1; //
BAUDCON2bits.BRG16=0; // 8 bit baud active 
SPBRG2=129;

while (1){
    
 LATAbits.LA0=1;
 delay(500);
 
 pc_write("Test") ; 
 
  LATAbits.LA0=0;
 delay(500);
  
  
}

}

解决方法

@Hesi 我已经在 MPLABX 模拟器中尝试过你的代码。我的 IDE 版本是 5.50，XC8 版本是 2.32。但它没有为以下配置编译您的原始代码：
#pragma config XINST = ON
出现此错误：

/opt/microchip/mplabx/v5.50/packs/Microchip/PIC18F-K_DFP/1.4.87/xc8/pic/include/proc/pic18f26k22.h:16684::错误：（1504）PIC18扩展指令set 已启用，但此编译器不支持

然后我将 config pragma 行修改为 XINST = OFF 并成功编译。它确实在 UART 窗口中输出字符。然而，在真实的物理世界中，有许多因素可能会影响 MCU 的行为。我认为您使用某种 RS232 电缆和电平转换器将电路连接到 PC。如果是这样，请确保您的中间设备连接正确且没有问题。您还可以采取其他几个步骤来调试电路：

  • 您可以使用示波器调试 MCU 的 TX 线
  • 如果不可能，您可以使用另一个 MCU 来测试您的 MCU，方法是将线路直接首尾相连。您可以编写一个测试程序，读取 UART 输入并将其显示在字符 LCD 上。

顺便说一下，这是您在 MCU 中使用的相同代码吗？在我正在工作的一个项目中，我有效地使用了 18F46K22 及其 USART2 外设来毫无问题地发送字节序列。如果有帮助，这就是我在 16 MHz 上启动它的方式：

// BRG16 = 1,BRGH = 1

// disable interrupts before changing states
PIE3bits.RC2IE = 0;
PIE3bits.TX2IE = 0;

// ABDOVF no_overflow; CKTXP async_noninverted_sync_fallingedge; BRG16 16bit_generator; WUE disabled; ABDEN disabled; DTRXP not_inverted; 
BAUDCON2 = 0x08;

// SPEN enabled; RX9 8-bit; CREN enabled; ADDEN disabled; SREN disabled; 
RCSTA2 = 0x90;

// TX9 8-bit; TX9D 0; SENDB sync_break_complete; TXEN enabled; SYNC asynchronous; BRGH hi_speed; CSRC slave_mode; 
TXSTA2 = 0x24;

// 9Fh @9600 bps ve @16 MHz
SPBRG2 = 0x9F;

// 1h @9600 bps ve @16 MHz
SPBRGH2 = 0x01;

// enable receive interrupt
PIE3bits.RC2IE = 1;
mcupicuartusart