使用PIC16F628A进行PWM所需的帮助

如果有人能给我一些帮助，让我知道如果我的计算/理解是正确的或不正确的，与配置PIC16F628 A PWM信号有关，这将是最有帮助的。我使用一个20MHz振荡器晶体与16F628 A，并试图通过RB3引脚输出PWM信号。在RB3上输出的ACH信号需要64微秒长，我计算为15625Hz（（1／64）x 1000000）。前4微秒设置为低/关（TOFF），剩下的60微秒设置为高/开（吨）。因此，我计算TOFF为6.25%和吨为93.75%。1。将PWM周期写入到PR2寄存器：15625Hz脉冲在93.75%占空比周期＝[PR2+1] 1×4×ToSc x TMR2预值，这可以被重新排列成：PR2= FoCC--------------------------1 fPultX time2 PrimeX-X4问题1：假设Fosc =实习生Al晶体频率为400 000 HZ问题2：我假设F脉冲＝15625HZQuasm 3的脉冲频率：我不理解为什么Time2 PraseL= 4PR2＝4000000 --------------- 1＝15×15625×4×42）设置CCPR1L:CCP1CON比特和5:4& gt；占空比（吨）占空比＝（CCPR1L）可将CCPR1L:CCP1CON位和5:4GT＝占空比X FoCC------------------TMR2预置值，其中CCPR1L:CCP1CON/LT；5:4/G.值在CCPR1L寄存器和比特4和BI中。t＝5＝0.9375＝0.00006＝93.75%（15625Hz的周期）：15625 CCPR1L：CCP1CON/LT；5:4＝0.00006×4000000＝---------= 60，现在将这个数转换为二进制＝0011 1100ccp1CON位4＝0，位5＝0CCPR1L= 90001111，因此，我的汇编代码是：使用MPLAB 8.92并加载上面的代码，将调试器工具设置为MPLAB SIM，打开模拟器逻辑分析器，并选择PIC16F628 AUPON的PIN RB3作为代码运行的通道，然后检查逻辑分析仪，我测量了X轴上的4个周期的TOFF和X轴上的60个周期的Ton，总共64个循环。问题4：这会产生在15625Hz的PIN RB3上的PWM信号（1/64个周期＝15626Hz）。如果不是，请你解释一下我误解了使用的方法（信息是从谷歌搜索得到的）。



      以下为原文

    It would be most helpful if someone could provide me with some help and let me know if my calculations / understandings are correct or incorrect, relating to configuring a PIC16F628A PWM signal.

I'm using a 20mhz oscillator crystal with the 16F628A and trying to output a PWM signal via the RB3 pin.

Each signal to be outputted on RB3 needs be 64 microseconds long, which i calculate to be 15625hz ((1/64us) x 1000000). The first 4 microseconds set to low/off (Toff) and the remaining 60 microseconds set to high/on (Ton). Therefore, I calculate Toff to be 6.25% and Ton to be 93.75%.

1. Set the PWM period by writing to the PR2 register: 15625hz pulse at a 93.75% duty cycle

Period= [PR2 + 1] x 4 x Tosc x TMR2-prescale-value
This can be rearranged to:
PR2=                   Fosc
          ---------------------------------  - 1
          Fpulse x Timer2-prescale x 4

QUESTION 1: I am assuming Fosc = the internal crystal frequency of 4000000hz
QUESTION 2: I am assuming Fpulse = frequency of pulse of 15625hz
QUESTIOM 3: I am not understanding why Timer2-prescale = 4

PR2=        4000000   
          -----------------  - 1    = 15
           15625 x 4 x 4

2) Set CCPR1L:CCP1CON bits<5:4> to the duty cycle (Ton)

Duty cycle= (CCPR1L:CCP1CON bits<5:4>) x Tosc x TMR2-prescale-value

This can be rearranged to:

CCPR1L:CCP1CON bits<5:4> =     Duty cycle x Fosc
                                                  --------------------
                                                TMR2-prescale-value

Where CCPR1L: CCP1CON<5:4> means- value in CCPR1L register and bit 4 and bit 5 of CCP1CON register

Duty cycle =  0.9375
                    --------  =  0.00006 (93.75% of period of 15625hz)
                    15625
      
CCPR1L: CCP1CON<5:4>=   0.00006 x 4000000
                                          ----------------------  = 60
                                                       4

Now convert this number to binary = 0011 1100
CCP1CON bit 4= 0, bit 5=0
CCPR1L= 00001111
Therefore, my assembly code is;

list p=16F628a
#include p16f628a.inc

;******************************************************************************************
__CONFIG _BOREN_OFF & _CP_OFF & _CPD_OFF & _PWRTE_ON & _WDT_OFF & _LVP_OFF & _MCLRE_ON & _HS_OSC

;******************************************************************************************
org 00h ; start address
goto START ; start of code
org 04h ; start address of interrupt
retfie ; start of interrupt code

;******************************************************************************************
START
movlw b'00000000' ; Sets inputs and output for PORTA
movwf TRISA ; Sets the ports for PORTA
banksel TRISA ; Change to the bank with TRISA
movlw b'00000000' ; Sets inputs and output for PORTB
movwf TRISB ; Sets the ports for PORTB
banksel PORTB

;STEP 1: Set the PWM period by writting to the PR2 register
;-------------------------------------------------------------------------------

banksel PR2
movlw d'15'
movwf PR2

;STEP 2: Set the PWM duty cycle by writing to CCPR1L & CCP1CON
;--------------------------------------------------------------------------------------------

banksel TMR2
movlw b'00001111'
movwf CCPR1L
movlw b'00001100'
movwf CCP1CON

;Set the TMR2 prescale value and enable TIMER2 by writing to T2CON
;----------------------------------------------------------------------------------------------

movlw b'00000101'
;                       01 Bit 0&1 control Prescale (00=1:1, 01=1:4, 1x=1:16 division)
;                     1     Bit 2: 1=Timer On, 0=Timer Off
;              0000      Bit 3 to 6 control Postscale (0000=1:1 division)

movwf T2CON

LOOP
goto LOOP
end


Using MPLAB 8.92 and loading the above code, setting the Debugger tool to MPLAB SIM, opening the Simulator Logic Analyser and selecting the channel as pin RB3 of the PIC16F628A

Upon running the code briefly and then examining the logic analyser, I measured the Toff at 4 cycles on the x-axis and Ton at 60 cycles on the x-axis, total 64 cycles.

QUESTION 4: Will this produce a PWM signal on pin RB3 of 15625hz (1/64 cycles = 15626hz). If not, could you please try to explain where i have misunderstood the method to use (information has been obtained from Google searching).

Many thanks
Adrian