Frequency Measure, Timer, Interupt 16F688

[Nobody/Anonymous]

Hi,
I appreciate this has been asked before, but am struggling to get this working, looking for some sample code and clarification i am looking to measure frequency (between about 5hz and 125hz) on one of the pins on a 16F688, i am completely confused with timers, interupts, prescalers, and cant even decide which pin to use now as input. (8 or 16bit and which pin?)

Any help appreciated.

[Nobody/Anonymous]

hi again, sorry, realised i may be asking a bit much here.
I realise (hopefully correctly) that i should be timing the time gap with a timer between interups, which gives me the data i need, i am confused about which input on the 16F688 to use, is it RA2? and just cant get any code working at all.

[Nobody/Anonymous]

I see no one is answering your questions.  I certainly don't have all the answers but would give you some advise.
You are asking about some of the more difficult topics in programming:  timing, counting and interrupts.
so break them up into  specific questions,  littler pieces.  Make a list of things you want to accomplish.

constraints so far:    16F688   which has two counters  T0 is 8 bit and T1 is 16 bit.  they both have prescalers if needed.
second you want to count   5 to 125 counts per second

so logically, maybe not practically, both counters can count this high…   8bit=256  16bit ~ 65535
if you want to be accurate, you will need a crystal oscillator to give a time period to count in,
by definition= counts/sec
both counters  can have a crystal osc source.   also there is a tunable internal clock
I just looked at the 16F688 spec sheet for clock source and it is a little confusing.

One of my favorite resources is PICList website.
Also  Microchip has a lot of good app notes and spec sheets with some examples.

Good Luck
Mike

[Nobody/Anonymous]

i meant to add this to last posting but forgot.

This is an example that I implemented for use in a sideral clock I built.
It  is the subroutines for the 1 sec interrupt.

' 32khz Clock crystal on T1 osc pins

#chip 16F886, 8

#config OSC = INTRC_IO

#define inchrs PORTC.3   ' clock seting buttons

#define incmin PORTC.4

#define incsec PORTC.5

RTCinit   ' sets up the interrupt

'Pin Direction

dir inchrs in

dir incmin in

dir incsec in

' Main Loop
'

'Sub routines

sub RTCinit

MOVLW 0x80 ; Preload TMR1 register pair

MOVWF TMR1H ; for 1 second overflow

CLRF TMR1L

BSF     INTCON, PEIE    ; Enable Peripheral Interrupts

BSF     INTCON, GIE     ; Enable all Interrupts

MOVLW b'00001111' ; Configure for external clock,

MOVWF T1CON ; Asynchronous operation, external oscillator

CLRF secs ; Initialize timekeeping registers

CLRF mins

MOVLW .12

MOVWF hours

Wait 5 10us

BSF PIE1, TMR1IE ; Enable Timer1 interrupt

end sub

sub INTERRUPT

BSF TMR1H, 7 ; Preload for 1 sec overflow

BCF PIR1, TMR1IF ; Clear interrupt flag

BSF     INTCON, PEIE    ; Enable Peripheral Interrupts

BSF     INTCON, GIE     ; Enable all Interrupts

secs = secs +1 ' Increment seconds

if  secs < 60 then goto fini  ' yes, done

secs = 0  'Clear seconds

mins = mins +1  ' Increment minutes

if  mins < 60 then goto fini  ' yes, done

mins = 0   ' clear minutes

hours = hours +1 ' Increment hours

if  hours < 24 then goto fini  ' yes, done

hours =0 ' Clear hours

fini:  'Done

end sub

I know this is a combination of assembler and GCBasic BUT that is one of the wonderful things about GCBasic.
I give credit to Microchip and one of the timer apps but I forgot which one.

Mike

[Nobody/Anonymous]

thanks for the reply, i guess my question and title was a bit wrong initially, i think what i meant to ask was:-

I want to measure frequency (between about 5hz and 125hz on a 16F688, i am assuming the best way is to measure the time interval between pulses with interupts (and then average them out), can someone point me in the right direction with a code example please of measuring time intervals with interupts?

[kent_twt4]

Here is a concise example on setting up the Timer interrupt, prescaler, and registers to overflow at a specific interval.  I would try that first and measure the ouput by blinking an led in Main after  X number of increments or overflows.  So for instance  try adding the code below to that example for a 1Hz signal.   After getting that going, then try something along the lines of a 50us, or 100us rollover for the 5Hz to 135Hz periods.

That will get you half the way there.  The other half would be to keep track of the signal edges and determining how many rollovers while polling a digital input (e.g. dir PortC.1 in).  Another  possibility is using a CCPx interrupt, if other things are happening in the program, check out the forum for an example.

#define led PortC.0
dir led out
Main:
'Main code
'Do something useful with TenthSeconds here
Do
If TenthSeconds = 5 Then Set led On
    'led = ! OnOff
    'TenthSeconds = 0
If TenthSeconds = 10 Then
    Set led Off
    TenthSeconds = 0
end if
Loop
goto Main

[mmotte]

Here is a working code!  
It is for the 16F887 because that  is the proto board I had to test on.
The interrupt does all the work.  Port D has 8 LEDS on the protoboard.
It is running in front of me right now and when I touch my metal pen to the RA4 input which is the T0CKI - T0 Clk input the LEDS on portD light up   00****00 …    that is binary for 60hertz!!  yahoo sometimes thing work

Good luck converting the code

'Frequecy read out on port D by 8 Leds

' Couter T0 counts the  pulses into RA4
'  Counter timer T1 interrupts every 1 sec because it has a 32khz clock crystal on it and acouple of caps and a resistor
' Read about the external T1 osc in the Microchip specs sheet
'

'1/29/2010  all rights reserved.. Mike Otte

#chip 16F887, 8 

#config INTOSC 

RTCinit

mins = 0

hours = 0

secs=0

'Pin Direction

DIR PORTD OUT    ' this is the frequency read out in binary

Mainloop:

' waste time her in main loop that does nothing

wait 1 s

'    

wait 1 s

Goto Mainloop

' ----------- Subrutines below -----------------

sub RTCinit

            CLRF    PIR1            ;

            MOVLW   0x0E

            MOVWF   T1CON           ; RC1 is overridden by TCKO

            BSF     INTCON, PEIE    ; Enable Peripheral Interrupts

            BSF     INTCON, RBIE    ; Disable PORTB<7:4> Change Interrupts

            BSF     INTCON, GIE     ; Enable all Interrupts

           

           

MOVLW b'11101000' ; Configure for external clock counting

MOVWF OPTION_REG 

MOVLW 0x80 ; Preload TMR1 register pair

MOVWF TMR1H ; for 1 second overflow

CLRF TMR1L

MOVLW b'00001111' ; Configure for external clock,

MOVWF T1CON ; Asynchronous operation, external oscillator

CLRF secs ; Initialize timekeeping registers

CLRF mins

MOVLW 12

MOVWF hours

Wait 5 10us

'BANKSEL PIE1

BSF PIE1, TMR1IE ; Enable Timer1 interrupt

end sub

sub INTERRUPT

'BANKSEL TMR1H

BSF TMR1H, 7 ; Preload for 1 sec overflow

BCF PIR1, TMR1IF ; Clear interrupt flag

BSF     INTCON, PEIE    ; Enable Peripheral Interrupts

BSF     INTCON, RBIE    ; Disable PORTB<7:4> Change Interrupts

BSF     INTCON, GIE     ; Enable all Interrupts

INCF secs, F ; Increment seconds

PortD = Tmr0
Tmr0 = 0

'If PORTD.3 = ON Then
' Set PORTD.3 OFF
' RETURN
'END IF
'Set PORTD.3 ON

RETURN ; Done

end sub

[Nobody/Anonymous]

thanks to all, forgot the mention Great Cow Basic is great, thanks to all for the work and help!