Using hardware capture

[rmteo]

Would it be possible for you to do a non-blocking version of Measuring signal pulse widths with capture module.

[Bruce]

Definitely. Just let CCP1 generate an interrupt, and handle flipping CCP1CON.0 + grabbing
results in T1/PW in the interrupt handler.

[rmteo]

OK, thanks.

[Bruce]

This should work;

' Measuring signal pulse widths with capture module & interrupt

' Procedure for high-going pulse:
' 1. Configure CCP to capture on rising edge
' 2. Setup Timer1 so it will not overflow during max pulse width time
' 3. Enable ccp capture
' 4. Once capture flag bit is set, save captured value as T1
' 5. Reconfigure CCP to capture on falling edge
' 6. On 2nd capture, save 2nd value as PW
' 7. Subtract T1 from PW for the pulse width value

  DEFINE OSC 4              ' 4MHz for 1uS resolution TMR1 counts
  DEFINE INTHAND CCP_INT    ' declare high-pri interrupt handler
    
  Symbol Capture = PIR1.2   ' CCP1 capture flag
  SYMBOL CapIE = PIE1.2     ' CCP1 interrupt enable bit
  SYMBOL CapPriEn = IPR1.2  ' priority enable bit for CCP1 interrupt
  SYMBOL PriEnable = RCON.7 ' set to enable priority levels on interrupts
    
  T1 VAR WORD BANKA SYSTEM ' 1st capture value
  PW VAR WORD BANKA SYSTEM ' 2nd capture value & ultimately final pulse width
  CF VAR BYTE BANKA SYSTEM ' indicates when last capture is ready

  CLEAR                ' clear RAM on POR
  TRISC.2 = 1          ' CCP1 input pin (Capture input on 18F242)
  INTCON = 0           ' Interrupts off for now

  GOTO Init            ' jump over interrupt handler
  
ASM
CCP_INT
  BTFSS CCP1CON,0      ; capture from rising edge?
  BRA Fall             ; no .. goto falling edge
  MOVFF CCPR1L, T1     ; get low capture byte into T1
  MOVFF CCPR1H, T1+1   ; get high capture byte into T1
  BRA IntExit          ; outta here
Fall
  MOVFF CCPR1L, PW     ; get low capture byte into PW
  MOVFF CCPR1H, PW+1   ; get high capture byte into PW
  BSF CF,0             ; indicate last capture
IntExit
  BTG CCP1CON,0        ; toggle between rising/falling edge captures
  BCF PIR1,2           ; clear capture interrupt flag bit
  RETFIE FAST          ; return/restore W, STATUS and BSR
ENDASM
    
Init: ' initialize a few things first
  CCP1CON = %00000101  ' Capture mode, capture on rising edge
  T1CON = 0            ' TMR1 prescale=1, clock=Fosc/4, TMR1=off
  TMR1H = 0            ' Clear high byte of TMR1 counter
  TMR1L = 0            ' Clear low byte
  PriEnable = 1        ' enable priority levels on interrupts
  Capture = 0          ' clear capture flag bit
  CapPriEn = 1         ' set CCP1 int to high priority
  CapIE = 1            ' enable the CCP1 capture interrupt
  INTCON = %11000000   ' global + peripheral ints enabled
  T1CON.0 = 1          ' Turn TMR1 on here

Main:
  ' do other stuff here as required
  IF CF.0 THEN         ' figure out & print result only after last capture
    PW = PW-T1         ' High pulse width = PW-T1
    CF.0 = 0           ' clear flag bit
    HSEROUT [DEC PW,"uS High",13,10]
  ENDIF
  
  GOTO Main
    
  END

[rmteo]

Thanks. I converted it to SF.

Device = 18F4620       
Clock = 4

Dim Capture As PIR1.2   ' CCP1 capture flag
Dim CapIE As PIE1.2     ' CCP1 interrupt enable bit
Dim CapPriEn As IPR1.2  ' priority enable bit for CCP1 interrupt
Dim PriEnable As RCON.7 ' set to enable priority levels on interrupts

Dim T1 As Word          ' 1st capture value
Dim PW As Word          ' 2nd capture value & ultimately final pulse width
Dim CF As Boolean       ' indicates when last capture is ready
Dim CCP1 As Word Absolute $fbe   ' Location of CCPR1H:CCPR1L

Interrupt IntHigh()
   if CCP1CON.0=1 then  ' Capture from rising edge?
      t1 = ccp1         ' Move word to T1     
   else
      pw = ccp1         ' Move word to PW
      cf = true         ' Indicate last capture
   end if
   CCP1CON.0 = not CCP1CON.0  ' toggle between rising/falling edge captures
   capture = 0          ' Clear capture interrupt flag bit
End Interrupt

Sub Init()
   CCP1CON = %00000101  ' Capture mode, capture on rising edge
   T1CON = 0            ' TMR1 prescale=1, clock=Fosc/4, TMR1=off
   TMR1H = 0            ' Clear high byte of TMR1 counter
   TMR1L = 0            ' Clear low byte
   PriEnable = 1        ' enable priority levels on interrupts
   Capture = 0          ' clear capture flag bit
   CapPriEn = 1         ' set CCP1 int to high priority
   CapIE = 1            ' enable the CCP1 capture interrupt
   INTCON = %11000000   ' global + peripheral ints enabled
   T1CON.0 = 1          ' Turn TMR1 on here
End Sub

' Main Program Entry
Init                    ' Initialization
TRISC.2 = 1             ' CCP1 input pin (Capture input on 18F4620)
Enable(IntHigh)         ' Enable Interrupts

While true
   ' do other stuff here as required
   If CF Then           ' figure out & print result only after last capture
      PW = PW-T1        ' High pulse width = PW-T1
      CF = false        ' Clear flag bit
      ' Send Out Data
   EndIf
Wend