Okay, I was curious about the actual speed my controller
is running at, so I ran the following loop on it. If I'm not mistaken,
I've set OSCCON to 8MHz, so at 4 clock/instruction I should see
0.5 uS pulses. My scope on RB4 shows pulses 5uS wide!

I'm out by a factor of 10. What have I not taken into account?


#include <p16F690.inc>
__config (_INTRC_OSC_NOCLKOUT & _WDT_OFF & _PWRTE_OFF & _MCLRE_OFF &
_CP_OFF & _BOR_OFF & _IESO_OFF & _FCMEN_OFF)

Org 0
goto Start
Org 4
goto ISR
ISR
retfie

Start movlw 0x71 ;b'01110001'
BANKSEL OSCCON
movwf OSCCON

; initialize any register that might affect I/O
BANKSEL IOCB
clrf IOCB
clrf WPUB
clrf ANSEL
clrf ANSELH

BANKSEL TRISA
clrf TRISA ; PORTA all output
clrf TRISB ; PORTB all output
clrf TRISC ; PORTC all output

BANKSEL SSPCON
bcf SSPCON, 5

;=== run timing loop ===
BSF PORTB,4
BCF PORTB,4
goto $-2
end

"randy.day" <randy.day@shaw.cax> wrote in message
news:nTedj.29074$DP1.13331@pd7urf2no...
> Okay, I was curious about the actual speed my controller
> is running at, so I ran the following loop on it. If I'm not mistaken,
> I've set OSCCON to 8MHz, so at 4 clock/instruction I should see
> 0.5 uS pulses. My scope on RB4 shows pulses 5uS wide!
>
> I'm out by a factor of 10. What have I not taken into account?
>
>
> #include <p16F690.inc>
> __config (_INTRC_OSC_NOCLKOUT & _WDT_OFF & _PWRTE_OFF & _MCLRE_OFF &
> _CP_OFF & _BOR_OFF & _IESO_OFF & _FCMEN_OFF)
>
> Org 0
> goto Start
> Org 4
> goto ISR
> ISR
> retfie
>
> Start movlw 0x71 ;b'01110001'
> BANKSEL OSCCON
> movwf OSCCON
>
> ; initialize any register that might affect I/O
> BANKSEL IOCB
> clrf IOCB
> clrf WPUB
> clrf ANSEL
> clrf ANSELH
>
> BANKSEL TRISA
> clrf TRISA ; PORTA all output
> clrf TRISB ; PORTB all output
> clrf TRISC ; PORTC all output
>
> BANKSEL SSPCON
> bcf SSPCON, 5
>
> ;=== run timing loop ===
> BSF PORTB,4
> BCF PORTB,4
> goto $-2
> end
>
>

The "goto $-2" takes two instruction times.
I make it as, (in 0.5uS steps and 0V,5V) ...
5-0-0-0-5-0-0-0-5-0-0-0-5-0-0-0-5 ...
I.e. 2uS repetition (500kHz), at a 1:3 duty cycle with 8MHz clock=2 mips.

"randy.day" <randy.day@shaw.cax> wrote in message
news:nTedj.29074$DP1.13331@pd7urf2no...
> Okay, I was curious about the actual speed my controller
> is running at, so I ran the following loop on it. If I'm not mistaken,
> I've set OSCCON to 8MHz, so at 4 clock/instruction I should see
> 0.5 uS pulses. My scope on RB4 shows pulses 5uS wide!
>
> I'm out by a factor of 10. What have I not taken into account?
>
>
> #include <p16F690.inc>
> __config (_INTRC_OSC_NOCLKOUT & _WDT_OFF & _PWRTE_OFF & _MCLRE_OFF &
> _CP_OFF & _BOR_OFF & _IESO_OFF & _FCMEN_OFF)
>
> Org 0
> goto Start
> Org 4
> goto ISR
> ISR
> retfie
>
> Start movlw 0x71 ;b'01110001'
> BANKSEL OSCCON
> movwf OSCCON
>
> ; initialize any register that might affect I/O
> BANKSEL IOCB
> clrf IOCB
> clrf WPUB
> clrf ANSEL
> clrf ANSELH
>
> BANKSEL TRISA
> clrf TRISA ; PORTA all output
> clrf TRISB ; PORTB all output
> clrf TRISC ; PORTC all output
>
> BANKSEL SSPCON
> bcf SSPCON, 5
>
> ;=== run timing loop ===
> BSF PORTB,4
> BCF PORTB,4
> goto $-2
> end
>
If you are only measuring the part of the pulse that is high, it appears it
should be 0.5 us. Check if your scope has a X10 horizontal magnification
switch (my old Leader has a knob on the inside of the Variable Possition
control (horizontal position) that is labeled, "PULL X10 MAG". Inadvertantly
activating that control can throw you off.

By the way, goto takes 2 instruction cycles, so you may be getting a 0.5 us
high pulse, followed by a 1 us low pulse.

Richard

Richard Seriani wrote:

[snip]

> If you are only measuring the part of the pulse that is high, it appears it
> should be 0.5 us. Check if your scope has a X10 horizontal magnification
> switch (my old Leader has a knob on the inside of the Variable Possition
> control (horizontal position) that is labeled, "PULL X10 MAG". Inadvertantly
> activating that control can throw you off.

ROFL! That's EXACTLY what it was!

I just got the scope last week as my early xmas present.
I'm going to be giggling over this for the rest of the night...

> By the way, goto takes 2 instruction cycles, so you may be getting a 0.5 us
> high pulse, followed by a 1 us low pulse.

Yep. The on/off ratio was correct, but it was all
*stretched* by a factor of 10, which seemed
suspicious on a base-8 micro, but I *never* would
have spotted that.

Cheers mate! You made my day!

"Randy Day" <randy.day@shaw.cax> wrote in message
news:4775A903.97662200@shaw.cax...
> Richard Seriani wrote:
>
> [snip]
>
>> If you are only measuring the part of the pulse that is high, it appears
>> it
>> should be 0.5 us. Check if your scope has a X10 horizontal magnification
>> switch (my old Leader has a knob on the inside of the Variable Possition
>> control (horizontal position) that is labeled, "PULL X10 MAG".
>> Inadvertantly
>> activating that control can throw you off.
>
> ROFL! That's EXACTLY what it was!
>
> I just got the scope last week as my early xmas present.
> I'm going to be giggling over this for the rest of the night...
>
>> By the way, goto takes 2 instruction cycles, so you may be getting a 0.5
>> us
>> high pulse, followed by a 1 us low pulse.
>
> Yep. The on/off ratio was correct, but it was all
> *stretched* by a factor of 10, which seemed
> suspicious on a base-8 micro, but I *never* would
> have spotted that.
>
> Cheers mate! You made my day!

Randy,

Glad to be able to help. Thanks for letting me know.

Happy New Year.

Richard