PIC16F628A脉冲计数器丢失脉冲边沿

您好，我正在尝试使用PIC16F628 A作为一个相当简单的频率计数器。我有两个脉冲-一个长脉冲的RB4（18.8毫秒长，107毫秒之间的脉冲），让我知道一个事件正在发生，另一个脉冲在RB7多次发生，而RB4是高。一旦我计算RB7的脉冲，而RB4是高的，我以简单的串行方式发送RB1的计数。107毫秒有足够的时间这样做而不干扰任何计数。电路是非常简单的- 20 MHz晶体与15个PF帽，5V电源，旁路电源帽，MCLR保持高通过10K电阻器，两个5V脉冲连接-RB4和RB7，以及串行输出线到计算机从RB1。我知道在RB7上使用示波器的脉冲串的一般性质-它非常接近方波- 5美国高，5.6美国低，所以一段时间为10.6美国（94.3千赫）。我的第一个程序如下：我的结果计数是570路太低！我只是不明白——当代码运行在20 MHz时，我应该足够快地执行这些命令（20 MHz / 4＝0.2命令），这样我就不会丢失脉冲边沿。因此，我重写了代码，而将timeR1用作异步计数器如下；该代码产生了我所期望的——每个事件大约1774个计数（18.8毫秒/ 10.6个US＝1774）。伟大的。但是我需要知道第一个程序到底是什么！有些东西不合算。我真正感到困惑的是，我知道RB7上的脉冲序列的性质随着时间的推移而变化，这是由于一些外部的影响。尽管计数从第一个程序是错误的，它确实表明了正确的变化！另一方面，第二个程序总是显示相同的数字-大约1774。我简直是不知所措！好的，谢谢你的阅读和评论。非常感谢你的任何想法。尊敬的Marshall。



      以下为原文

    Hello,
I am trying to use a PIC16F628A as a fairly simple frequency counter. I have two pulses - one long pulse on RB4 (18.8 ms long, 107 ms between pulses) that lets me know an event is occurring, and another pulse on RB7 that occurs multiple times while RB4 is high. Once I count the pulses of RB7 while RB4 is high, I transmit the count out of RB1 in a simple serial fashion. 107 ms is plenty of time to do so without interfering with any counting.

The circuit is extremely simple - 20 MHz crystal with 15 pf caps, 5v supply, bypass power cap, MCLR held high through a 10k resistor, two 5v pulse connections - RB4 and RB7, and a serial output line to a computer from RB1.

Also, I know the general nature of the pulse train on RB7 using an oscilloscope - it's pretty close to a square wave - 5.0 uS high, 5.6 uS low, so a period of 10.6 uS (94.3 kHz).

My first program is as follows;

#define _XTAL_FREQ 20000000
#define bit0 1

#define bdr 14 // Sets baud rate to 57,600

#include
#include

// BEGIN CONFIG
#pragma config FOSC = HS // Oscillator Selection bits (HS oscillator)
#pragma config WDTE = OFF // Watchdog Timer Enable bit (WDT enabled)
#pragma config PWRTE = OFF // Power-up Timer Enable bit (PWRT disabled)
#pragma config BOREN = ON // Brown-out Reset Enable bit (BOR enabled)
#pragma config LVP = OFF // Low-Voltage (Single-Supply) In-Circuit Serial Programming Enable bit (RB3 is digital I/O, HV on MCLR must be used for programming)
#pragma config CPD = OFF // Data EEPROM Memory Code Protection bit (Data EEPROM code protection off)
#pragma config CP = OFF // Flash Program Memory Code Protection bit (Code protection off)
#pragma config MCLRE = ON
//END CONFIG

void sendSerialByte(unsigned char data)
{
    unsigned char i;
    i = 8;
   
    RB1 = 0; // set start bit
    __delay_us(bdr); // wait a full bit time
   
    while (i)
    {
        if (bit0 & data) // Check the value of the first bit in
        {
            RB1 = 1; // data, invert it, and put it out on the wire.
        }
        else
        {
            RB1 = 0;
        }
        
        data = data >> 1; // Rotate the data one to the right
        i--; // Decrement the counter
        
        __delay_us(bdr); // wait a full bit time
    }
   
    RB1 = 1; // set stop bit
    __delay_us(bdr); // wait a full bit time
    __delay_us(bdr); // wait a full bit time
    __delay_us(bdr); // wait a full bit
    __delay_us(bdr); // wait a full bit time
   
}

int main()
{
    unsigned int freqCtr = 0;
    unsigned char lowerPart;
    unsigned char upperPart;
    int state = 0;
    int sigVal;
   
    TRISB1 = 0; // Use RB1 as an output pin for serial
  
    TRISB7 = 1; // Use B7 bit as an input - pulse to be counted
    TRISB4 = 1; // Use B4 bit as in input - indicates valid info on B7
  
    // Send a few wake up # characters...
    sendSerialByte(35);
    sendSerialByte(35);
    sendSerialByte(35);
  
    while(1)
    {
        while (RB4)    // RB4 pulse is high, so count leading edges on RB7
        {
            sigVal = RB7;    // get the value of RB7
            if (sigVal != state)    // compare RB7 to the current state
            {
                if (sigVal == 1)    // RB4 must be high and since sigVal is 1 and sigVal != state, this is an edge!
                {
                    freqCtr++;    // Count the edge
                    state = 1;    // Change the state from 0 to 1 so I don't count this pulse anymore
                }
                else
                {
                    state = 0;    // pulse just ended, set the state back to 0
                }
            }
        }
   
        if (freqCtr > 0)    // don't bother reporting any zero data
        {
            lowerPart = freqCtr & 255;
            upperPart = (freqCtr & 65280) >> 8;
            sendSerialByte(60);
            sendSerialByte(lowerPart);
            sendSerialByte(upperPart);
            sendSerialByte(62);

            freqCtr = 0;    // reset the frequency counter after it's reported.
        }
    }
  return 0;
}

My resulting count is 570 - way too low! I just don't get it - with the code running at 20 MHz, I should be executing these commands fast enough (20 MHz/4 = 0.2 uS per command) so that I'm not missing pulse edges. So, I rewrote the code and instead used the Timer1 as an asynchronous counter as follows;

#define _XTAL_FREQ 20000000
#define bit0 1

#define bdr 14    // Sets baud rate to 57,600

// PIC16F628A Configuration Bit Settings

// 'C' source line config statements

// CONFIG
#pragma config FOSC = HS // Oscillator Selection bits (HS oscillator: High-speed crystal/resonator on RA6/OSC2/CLKOUT and RA7/OSC1/CLKIN)
#pragma config WDTE = OFF // Watchdog Timer Enable bit (WDT disabled)
#pragma config PWRTE = OFF // Power-up Timer Enable bit (PWRT disabled)
#pragma config MCLRE = ON // RA5/MCLR/VPP Pin Function Select bit (RA5/MCLR/VPP pin function is MCLR)
#pragma config BOREN = ON // Brown-out Detect Enable bit (BOD enabled)
#pragma config LVP = OFF // Low-Voltage Programming Enable bit (RB4/PGM pin has digital I/O function, HV on MCLR must be used for programming)
#pragma config CPD = OFF // Data EE Memory Code Protection bit (Data memory code protection off)
#pragma config CP = OFF // Flash Program Memory Code Protection bit (Code protection off)

// #pragma config statements should precede project file includes.
// Use project enums instead of #define for ON and OFF.

#include
#include

void sendSerialByte(unsigned char data)
{
    unsigned char i;
    i = 8;
   
    RB1 = 0; // set start bit
    __delay_us(bdr); // wait a full bit time
   
    while (i)
    {
        if (bit0 & data) // Check the value of the first bit in
        {
            RB1 = 1; // data, invert it, and put it out on the wire.
        }
        else
        {
            RB1 = 0;
        }
        
        data = data >> 1; // Rotate the data one to the right
        i--; // Decrement the counter
        
        __delay_us(bdr); // wait a full bit time
    }
   
    RB1 = 1; // set stop bit
    __delay_us(bdr); // wait a full bit time
    __delay_us(bdr); // wait a full bit time
    __delay_us(bdr); // wait a full bit
    __delay_us(bdr); // wait a full bit time
   
}

void main(void) {
    int state = 0;
   
    /*
    REGISTER 7-1: T1CON ? TIMER1 CONTROL REGISTER (ADDRESS: 10h)
     * B7 B6 B5 B4 B3 B2 B1 B0
        ? ? T1CKPS1 T1CKPS0 T1OSCEN T1SYNC TMR1CS TMR1ON
     * 0 0 0 0 1 1 1 x
     *
     * B7 not used
     * B6 not used
     * B5/B4 prescale select bits - 00 for 1:1
     * B3 Oscillator enable, set to 1 for input on RB7, set to 0 for input on RB6
     * B2 set to 1 for asychronous counter mode
     * B1 set to 1 for counter mode, not internal timer mode
     * B0 enable timer
     *
     * 0 0 0 0 1 1 1 0 --> 0010 1110
     * T1CON = 14, set up properly
     * T1CON = 15, set up properly
     *
     */

    T1CON = 14; // set up Timer1, turn it off
    TMR1H = 0; // set the timer value to 0
    TMR1L = 0;
   
    TRISB1 = 0; // set B1 up for output - serial data out (pin 7)
    TRISB4 = 1; // set B4 up for input - used for the slow pulse (pin 10)
    TRISB7 = 1; // set B7 up for input - used for the counted pulse (pin 13)
                    // I believe this value gets overridden anyway...
   
    sendSerialByte(35); // Send ### to say we are alive!
    sendSerialByte(35);
    sendSerialByte(35);
   
    state = 0; // Set the state to 0
    while (1) // Repeat forever
    {
        while (RB4) // While the slow pulse is high
        {
            if (state == 0) // This condition occurs if RB4 was just detected as high - basically a rising edge detector
            {
                T1CON = 15; // Turn on the counter
                state = 1; // Set the state to 1 - now this loop repeats until RB4 drops
               
                RB3 = 0; // Turn RB3 off - RB3 should be the inverse of the slow pulse present at RB4
            }
        }
        
        if (state == 1) // State JUST changed - send the data, but only once
        {
            T1CON = 14; // RB4 has dropped! Turn off the counter
        
            sendSerialByte(60); // Send first delimiter
            sendSerialByte(TMR1L); // Send counter low byte
            sendSerialByte(TMR1H); // Send counter high byte
            sendSerialByte(62); // Send second delimiter
        
            state = 0; // Turn off the state in preparation for the next time around
                                        // and to make sure we don't send another message for this count
            
            TMR1L = 0; // Reset the counter
            TMR1H = 0;
        }

    }
    return;
}

This code produces exactly what I'd expect - about 1,774 counts per event (18.8 ms/10.6 uS = 1,774). Great. But I need to understand exactly what that first program is counting! Something just doesn't add up.

What's really perplexing to me is that I know that the nature of the pulse train on RB7 changes over time due to some external influences. Despite the count being wrong from the first program, it does indicate the change properly! On the other hand, the second program always shows the same number - about 1,774. I am simply at a loss!

Ok, thanks in advance for reading and commenting - any and all thoughts are greatly appreciated.


Respectfully,
Marshall

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