program RPM_Counter

' variables declaration
Dim i, j, UART_Byte, Over_Flow, Averaging As Byte
Dim Digit as Byte[5]
Dim T As Longint[2]
Dim Capture As word absolute $15
Dim RPM, Period As Longint

'sub procedure procedure_name ' procedures declaration
sub procedure interrupt

 if TestBit(PIR1,CCP1IF) = 1 then     'Capture mode Interrupt Flag
  IF i > 1 Then
   i = 0
  End if
  
  T[i] = ( (Over_Flow *  65535) +  Capture )
   
  Inc(i)
  PIR1.CCP1IF = 0
 end if

 if TestBit(PIR1,TMR1IF) = 1 then     'TMR1 Interrupt Flag
  Inc(Over_Flow)
  PIR1.TMR1IF = 0
 end if
 
end sub

Sub procedure Delay_313
 Delay_ms(313)
End Sub
'end sub


'sub function function_name ' functions declaration

'end sub
main:                       ' main program body
 Delay_313                  'For Stability in Supply
 TRISC   = 255              ' PORTC all Inputs
 PORTC   = 0                ' PORTC = 0
 T1CON   = %00110000        'TIMER1 CONTROL REGISTER
 CCP1CON = %00000101
 INTCON.GIE  = 1
 INTCON.PEIE = 1
 Averaging   = 0
 USART_init(19200) ' initialize USART module
 
Reset_All:
 PIE1.CCP1IE  = 0           'CCP1 Interrupt Enable bit
 T1CON.TMR1ON = 0           'Timer1 On bit
 TMR1H        = 0
 TMR1L        = 0
 Over_Flow    = 0
 
ReStart:
 T1CON.TMR1ON = 1           'Timer1 On bit
 PIE1.CCP1IE  = 1           'CCP1 Interrupt Enable bit
 Delay_313                  'Aquire The values of T0 and T2

Convert_RPM:
 Period = T[1] - T[0]       'Subtract saved captured time (T0) from
                            'captured time (T1) and store
 
 IF Averaging = 1 Then      'if CCP1CON = every 16 edge the divide by 16
    Period = Period / 16
 End IF
 
 IF Period < 75000 Then    ' If RPM > 500 then next time
 CCP1CON = %00000111       ' Caculate every 16th Egde
 Averaging = 1             ' and Measure RPM with Averaging
 else                      ' IF RPM < 500 then next time
 CCP1CON = %00000101       ' calculate every rising edge
 Averaging = 0             ' Measure RPM without Averaging
 End If
 
 RPM = 37500000 / Period   'Convert Time Period in Round/Minute

Into_Digit:
 Digit[0] = RPM Div 10000 mod 10
 Digit[1] = RPM Div 1000  mod 10
 Digit[2] = RPM Div 100   mod 10
 Digit[3] = RPM Div 10    mod 10
 Digit[4] = RPM           mod 10
 
UsartWrite:
   Usart_Write(0x52)                   ' "R" For indication of RPM
   For j = 0 To 4 step 1
   UART_Byte = Digit[j] + 48           ' Add 48 for converting into ASCII
   Usart_Write(UART_Byte)
   Next j
   Usart_Write(0x0D)                   'CR
   Usart_Write(0x0A)                   'LF

Goto Reset_All
end. ' end of program

Connected to COM2
Received: R00867

Received: R0/*(-

Received: R00(*)

Received: R01682

Received: R0/*)'

Received: R00(*)

Received: R01679

Received: R00867

Received: R00(*(

Received: R01680

Received: R00867

Received: R0/*)'

Received: R01681

Received: R00867

Received: R0/*(.

Received: R00(*)

Received: R00867

Received: R0/*)'

Received: R00(*)

Received: R01679

Received: R00867

Received: R00(*(

Received: R01681

Received: R00867

Received: R0/*(0

Received: R01681

Received: R00867

Received: R0/*(.

Received: R00(*)

Received: R00867

Received: R0/*)'

Received: R00(**

Received: R01679

Received: R00867

Received: R00(*(

Received: R01681

Received: R00867

Received: R0/*(0

Device = 16F877
Xtal = 4
   		   
Dim uS as DWord
Dim Took_To_Long as Bit

Symbol GIE = INTCON.7				' Global Interrupt Enable Bit

Symbol Timer1 = TMR1L.WORD			' A special way of addressing both TMR1L and TMR1H with one register
Symbol TMR1_Enable = PIE1.0			' TMR1 interrupt enable
Symbol TMR1_Overflow = PIR1.0			' TMR1 overflow flag
Symbol TMR1_On = T1CON.0			' Enables TMR1 to start incrementing

Declare SERIAL_BAUD 19200
Declare RSOUT_PIN PORTA.1
Declare RSOUT_MODE TRUE
Declare RSOUT_PACE 5
			
ON_INTERRUPT Int_Sub

Goto Initialization			
			
Int_Sub:
	
	GIE = 0			
			
	If TMR1_Overflow = 1 And TMR1_Enable = 1 Then
		Took_To_Long = 1
		TMR1_Overflow = 0
	EndIf	
	
	GIE = 1
	
	Context Restore
	
Initialization:	

	ALL_DIGITAL = True
	
	High PORTA.1
	TRISA.0 = 1
	
	TMR1_Enable = 0
	GIE = 0
		
	INTCON.6 = 1   	  	' Peripheral Interrupts

	T1CON.1 = 0		' 1 = External clock from pin RC0/T1OSO/T1CKI (on the rising edge)
			   	' 0 = Internal clock (FOSC/4)

	T1CON.2 = 1		' 1 = Do not synchronize external clock input
			   	' 0 = Synchronize external clock input
				' When T1CON.1 = 0;
				'   this bit is ignored. Timer1 uses the internal clock when TMR1CS = 0.
					  	
	T1CON.4 = 1		' 11 = 1:8 prescale value
	T1CON.5 = 1		' 10 = 1:4 prescale value
				' 01 = 1:2 prescale value
				' 00 = 1:1 prescale value
	TMR1_Overflow = 0
	
	RSOUT "On",13
	
	TMR1_On = 0	  	  	' Disable TMR1 counting		
	TMR1_Enable = 1			' Enable TMR1 interrupts
	GIE = 1		  		' Enable Global Interrputs			
	
Main:

	Repeat

	Until PORTA.0 = 0		' Wait for PORTA.0 to go Low
	
	Repeat

	Until PORTA.0 = 1		' Wait for PORTA.0 to go high
	
	' The above two loops ensure we are not entering a pulse mid way, but on
	'   an actual rising edge
	
	Timer1 = 0			' Reset TMR1						  
	TMR1_On = 1	  	  	' Enable TMR1 counting			  	

	Repeat 

	Until PORTA.0 = 0 Or Took_To_Long = 1

	Repeat 

	Until PORTA.0 = 1 Or Took_To_Long = 1

	' The above 2 Repeat loops wait for a full cycle to occur
	
	TMR1_On = 0	  	  	' Disable TMR1 counting	

	If Took_To_Long = 1 Then	' Check if a time out occured
	    Took_To_Long = 0
		Goto Main
	Else
		Timer1 = Timer1 - 2	' Number of instructions that are executed while timed
			   	 	'  outside of pulse period
		uS = Timer1 * 8	  	' 1:8 prescaler & 4Mhz clock there for uS = Timer1 * 8
		RSOut "Period = ", Dec uS, " uS", 13
		RSOut "Frequency = ", Dec(1000000 / uS), " Hz", 13
		RSOut "RPM = ", Dec(1000000 / uS * 60), 13, 13
		Goto Main
	EndIf