Counter not counting !!!

[Archangel]

As Joe already mentioned earlier, RA4 T0CKI is a Schmitt Trigger input. If your sensor doesn't output a minimum voltage of 0.8 * VDD for logic 1 and 0.2 * VDD or less for logic 0, then the Schmitt Trigger input isn't seeing the correct logic levels, and TMR0 isn't counting your pulses.

Here's a quick little test program to show how it works when RA4/T0CKI is connected to an I/O-pin to increment the counter.

@ DEVICE pic16F88, INTRC_OSC, CCPMX_ON, MCLR_OFF

DEFINE HSER_BAUD 2400

Loops VAR BYTE
Revs var BYTE

OSCCON=$60 ' use internal 4MHZ osc

ANSEL = 0  ' disable A/D so RA4 is digital
CMCON = 7  ' disable comparators

TRISA.4=1  ' RA4/T0CKI = input (Timer0 clock input)
PORTB.5=1  ' USART TX pin idles high
PORTB.0=1  ' clock output pin to RA4 starts high
TRISB.0=0  ' clock out pin to RA4/T0CKI = output
TRISB.5=0  ' USART TX = output

ANSEL = 0     ' disable A/D so RA4 is digital
CMCON = 7     ' disable comparators
OPTION_REG = %10110001 ' clk on RA4/T0CKI, falling edge, 1:4 prescale

Mainloop:
    TMR0 = 0      ' clear count before each pass
    
    ' output 8 clocks on RB0 to RA4/T0CKI
    FOR Loops = 0 TO 7
      PORTB.0=1   ' RB0 connects to RA4/T0CKI
      PAUSE 5
      PORTB.0=0   ' counter increments on falling edge
      PAUSE 5
    NEXT Loops
      
    Revs = TMR0   ' get TMR0 count
    IF OPTION_REG.0 THEN
       HSEROUT ["Counts at 1:4 prescale: ",dec Revs,13,10]
    ELSE
       HSEROUT ["Counts at 1:2 prescale: ",dec Revs,13,10]
    ENDIF
    OPTION_REG.0 = OPTION_REG.0 ^ 1 ' toggle 1:4 or 1:2 prescale
    GOTO Mainloop 
    
    end

It works great, but only as long as the input signal meets the threshold levels the Schmitt Trigger input buffer on RA4/T0CKI expects.

I learned something again! I thought Schmitt trigger would switch at 3v, so 80 percent huh? I'm going to write that down. Thanks Bruce !

[lerameur]

Hi

well I am only getting about 3volt, so 0.8 * 5v = 4v, one volt away from triggering. I will a simple amplifier or inverter to the output of my sensor and feed that to the chip

ken

[lerameur]

I think I am getting there but just not quite.
your program works with the loop for incrementing. I removed the loop , because I have a sensor output, The output is going through an inverter, so now I get either 0 or 5v going into RA4.
What I now see on the LCD is the incrementation going up high without any look at the input. it goes up to a 1000 in about 3 seconds with the sensor laying there not moving:

Here is the code I have, mainly Bruce,s code with the addition of the LCD and external oscillation.


@ DEVICE pic16F88, CCPMX_ON, MCLR_OFF

DEFINE OSC 20 'use external 20mhz crystal
ANSEL = 0 ' disable A/D so RA4 is digital
CMCON = 7 ' disable comparators

TRISA.4=1 ' RA4/T0CKI = input (Timer0 clock input)

ANSEL = 0 ' disable A/D so RA4 is digital
CMCON = 7 ' disable comparators
OPTION_REG = %10110001 ' clk on RA4/T0CKI, falling edge, 1:4 prescale

Revs var BYTE
ORevs var word
Counter var word

'/////////////////////////
'// LCD configuration //
'/////////////////////////

DEFINE LCD_DREG PORTB ' Set LCD Data port
DEFINE LCD_DBIT 4 ' Set starting Data bit (0 or 4) if 4-bit bus
DEFINE LCD_RSREG PORTB ' Set LCD Register Select port
DEFINE LCD_RSBIT 1 ' Set LCD Register Select bit
DEFINE LCD_EREG PORTB ' Set LCD Enable port
DEFINE LCD_EBIT 0 ' Set LCD Enable bit
DEFINE LCD_BITS 4 ' Set LCD bus size (4 or 8 bits) '4 therefore put wire at 4, 5, 6 and 7 of LCD
DEFINE LCD_LINES 2 ' Set number of lines on LCD
DEFINE LCD_COMMANDUS 2500
DEFINE LCD_DATAUS 250
DEFINE CHAR_PACING 2000
pause 1000

Counter =0

Mainloop:
TMR0 = 0 ' clear count before each pass

' output 8 clocks on RB0 to RA4/T0CKI
'instead, input from sensor


Revs = TMR0 ' get TMR0 count
Counter = Revs + 1
IF OPTION_REG.0 THEN
LCDOUT $FE,1,"Counter1: ", DEC Counter
ELSE
lcdout $FE,$C0, "Counter2: ", DEC Counter
ENDIF
OPTION_REG.0 = OPTION_REG.0 ^ 1 ' toggle 1:4 or 1:2 prescale
GOTO Mainloop

end

[lerameur]

Hi,

also, I used your program andn it seemed to work but I realized that even if I remove the Loop: (or simply remove the connection between RA4 and RB3)
FOR Loops = 0 TO 7
PORTB.3=1 ' RB0 connects to RA4/T0CKI
PAUSE 5
PORTB.3=0 ' counter increments on falling edge
PAUSE 5
NEXT Loops

the incrementation stays the same change, so I guess there si not effect on TMR0.

K

[Bruce]

Try this;

Mainloop:
TMR0 = 0 ' clear count before each pass
PAUSE 5000 ' give it some time to count pulses
Revs = TMR0 ' get TMR0 count
Counter = Counter + 1
LCDOUT $FE,1,"Counter1: ", DEC Counter
LCDOUT $FE,$C0, "Revs: ", DEC Revs
GOTO Mainloop

Counter of course is always going to change every 5 seconds or so, but Revs shouldn't until you have pulses in on RA4.

Timer0 will automatically count pulses. You don't need to check any regs, bits, etc, just read it & clear it as required.

[lerameur]

I did output the Revs and it increment without any input:
not as fast, takes about 2 seconds to get to ten.
The odd thing is that it increment without changes to RA4.
I am going to try your code you posted and be back later
thanks for your time

Mainloop:
TMR0 = 0 ' clear count before each pass

' output 8 clocks on RB0 to RA4/T0CKI
'instead, input from sensor


Revs = TMR0 ' get TMR0 count
Counter = Revs + 1
IF OPTION_REG.0 THEN
LCDOUT $FE,1,"Revs: ", DEC Revs
ELSE
lcdout $FE,$C0, "Counter2: ", DEC Counter
ENDIF
OPTION_REG.0 = OPTION_REG.0 ^ 1 ' toggle 1:4 or 1:2 prescale

GOTO Mainloop

end

[lerameur]

Hi again

I set my function generator to 100Hz and the Revs outputs 127, when I set it to 1000Hz, I get Revs 225 on my LCD.
I get a specific number to from different frequency input.

Ken

[Bruce]

That's a good sign. Higher frequency should = a higher count in a given time period.

FYI: You really don't need to keep flipping OPTION_REG.0. That was just a part of my
previous example to show the count difference with different prescaler values. I would
leve it set at one prescale if you want valid counts.