Counting Timer0 and Timer1 overflows without any interrupt handler

[Darrel Taylor]

For this project ... you should not be using interrupts.
Especially not ON INTERRUPT. There's no guaranteed timing with ON INTERRUPT.

207 isn't a good value to load in the Timer.
Since the Timer will normally overflow in 65536 counts, you just need to set bit-7 of the high byte to make it overflow in 32768 counts.
With a 32768 Hz crystal, it will overflow in exactly 1 second.

Timer1 doesn't free-run. You need to stop and start it so that you can synchronize the Timer0 Gate output with Timer1's 1 second window.

Since the PIC's changed now, the oscillator's changed and interrupts are introduced ...
I think I'll just post my code for the 877A simulation in post #5.
Hopefully you can convert it for your needs with a different PIC.

; DT_FREQy.pbp
;
; Created     : Mon Feb 3 2014
; Processor   : PIC16F877A
; Compiler    : PicBasic Pro 3.0

;----[Device Configuration]--(See manual section 4.9)---------------------------
#CONFIG
  __config  _HS_OSC & _WDT_OFF & _PWRTE_OFF & _BODEN_OFF & _LVP_OFF & _CPD_OFF & _WRT_OFF & _DEBUG_OFF & _CP_OFF
#ENDCONFIG

;----[DEFINEs]------------------------------------------------------------------
DEFINE OSC 20

DEFINE LCD_DREG PORTD         ; LCD data port
DEFINE LCD_DBIT 4             ; LCD data starting bit 0 or 4
DEFINE LCD_RSREG PORTD        ; LCD register select port
DEFINE LCD_RSBIT 2            ; LCD register select bit
DEFINE LCD_EREG PORTD         ; LCD enable port
DEFINE LCD_EBIT 3             ; LCD enable bit
DEFINE LCD_BITS 4             ; LCD bus size 4 or 8
DEFINE LCD_LINES 2            ; LCD Number lines on LCD
DEFINE LCD_COMMANDUS 2000     ; LCD Command delay time in us
DEFINE LCD_DATAUS 50          ; LCD Data delay time in us

;----[Aliases]------------------------------------------------------------------
Timer1    VAR WORD EXT : @Timer1 = TMR1L
TMR0IF    VAR INTCON.2
TMR0CS    VAR OPTION_REG.5
TMR1IF    VAR PIR1.0
TMR1CS    VAR T1CON.1         ; Timer1 Clock Source Select bit
T1OSCEN   VAR T1CON.3         ; Timer1 Oscillator Enable Control bit
TMR1ON    VAR T1CON.0         ; Timer1 On bit
T1OSI     VAR PORTC.1         ; 32768 Hz input pin
PSCLKOUT  VAR PORTA.3         ; pin to clock out the remaining prescaler
PSA       VAR OPTION_REG.3    ; Prescaler Assignment bit

;----[Variables]----------------------------------------------------------------
Result     VAR WORD[2]        ; Final 32-bit Frequency measurement
T0overflow VAR Result[1]      ; Counts Timer0 overflows (HighWord of the result)
T0value    VAR Result.BYTE1   ; Final Timer0 value
PScount    VAR Result.BYTE0   ; Final Timer0 Prescaler value

FreqHigh   VAR WORD           ; Top five digits of the decimal result
FreqLow    VAR WORD           ; Bottom 3 digits of the decimal result
MeasCount  VAR WORD           ; Counts number of measurements

;----[Initialize]---------------------------------------------------------------
ADCON1 = 7                    ; All Digital
CMCON  = 7
T1OSCEN = 1                   ; Start Timer1 oscillator
PAUSE 250                     ; LCD Power-Up delay 
LCDOUT $FE,1,"DT's FREQy"
MeasCount = 0                 ; clear the measurement count

;----[Main Program Loop]--------------------------------------------------------
Main:
    GOSUB MeasureFreq         ; Get a Frequency Measurement
    GOSUB DisplayFreq         ; Display the Frequency

    MeasCount = MeasCount + 1 ; increment and display measurement count
    LCDOUT $FE,$94,"Meas = ", DEC MeasCount
GOTO Main

;----[Measure frequency on T0CKI]-----------------------------------------------
MeasureFreq:
    LOW PSCLKOUT          ; prevent signal from getting to Timer0
    PSA = 0               ; Prescaler is assigned to the Timer0 module
    TMR0CS = 1            ; Transition on T0CKI pin
    TMR1CS = 1            ; Timer1 Clock source = T1CKI (T1OSC)
    TMR1ON = 0            ; Stop Timer1
    TMR0IF = 0            ; Clear Timer0 overflow flag
    T0overflow = 0        ; Clear Timer0 overflow count
    TMR0 = 0              ; Clear Timer0 value

    Timer1 = $FFFF        ; Timer1 overflows on next cycle of 32768 Hz clock
    TMR1IF = 0            ; Clear Timer1 overflow flag
    TMR1ON = 1            ; Start Timer1 1 sec. period
    WHILE !TMR1IF : WEND  ; Synchronize to 32768 clock
    INPUT PSCLKOUT        ; Start counting freq input
    Timer1.15 = 1         ; Set Timer1 to 32768 for 1 Sec. period
    TMR1IF = 0            ; Clear Timer1 overflow flag

    WHILE !TMR1IF         ; while 1 sec. window is open  ---|
        IF TMR0IF THEN    ; count TMR0 overflows            | This section
            T0overflow = T0overflow + 1  ;                  | does the actual
            TMR0IF = 0                   ;                  | 1-Sec measurement
        ENDIF                            ;                  | Window
    WEND                                 ;               ---|
    LOW PSCLKOUT           ; Stop further counting
    T0value = TMR0         ; get Timer0 value

    PScount = 0            ; Clock out remaining prescaler
    WHILE TMR0 = T0value   ; until TMR0 value changes
        HIGH PSCLKOUT
        PAUSEUS 3
        LOW PSCLKOUT
        PAUSEUS 3
        PScount = PScount + 1
    WEND
    PScount = -PScount     ; negate to get prescaler count
RETURN

;----[Display frequency on LCD]-------------------------------------------------
DisplayFreq
    R2 = Result            ; Load Result into PBP's system vars for DIV32
    R0 = Result[1]
    FreqHigh = DIV32 1000  ; get left most 5 digits
    FreqLow = R2           ; remainder (R2) is right 3 digits

    LCDOUT $FE,$C0,"Freq = "
    IF FreqHigh > 0 THEN                        ; if any left digits
        LCDOUT DEC FreqHigh, DEC3 FreqLow,"   " ; display both left and right
    ELSE                                        ;  otherwise 
        LCDOUT DEC FreqLow,"     "              ; display only right digits
    ENDIF
RETURN

END