how to divide oscillator frequency?

[hiren.dave@bhuved.com]

hi,

i am using pic 18f46j11 microcontroller. my controller gives 5 times delay. i used 20mhz crystal. now if i delay particular port to 1 instruction than it gives 1us instead of 200ns. (20mhz/4=5 mhz=200ns).

i want to give delay of 200ns. how can i do that?

 

[Ian Rogers]

What language are you using.... in asm you use "nop" in "C" we use Nop(); both give a 1 instruction delay..

 

[Jon Wilder]

If you're only getting 1uS delay for a nop instruction, it sounds like your PIC doesn't know that it has a crystal on its pins. How did you set up your configuration words?

 

[hiren.dave@bhuved.com]

hi..

i am using assembl language.

i want to on LED on portd for 200ns.

if i write instruction

SETF PORTD
CLRF PORTD

than, between these instruction port must be on for 200ns (20 mhz crystal) but it takes 1 us for remaing on.

simply,

i want to on portd for just 200ns and 2 second off.

how should i do that??

 

[Jon Wilder]

hi..

i am using assembl language.

i want to on LED on portd for 200ns.

if i write instruction

SETF PORTD
CLRF PORTD

than, between these instruction port must be on for 200ns (20 mhz crystal) but it takes 1 us for remaing on.

simply,

i want to on portd for just 200ns and 2 second off.

how should i do that??

How are you setting your configuration word???

 

[hiren.dave@bhuved.com]

Osc = hs

 

[Ian Rogers]

i want to on LED on portd for 200ns.

You would never see it........ Its probably quicker than the LED's on time...

Is it an IR application?

 

[circuitspecialists]

How are you measuring the output pulse width? You should also try to measure the actual instruction clock frequency by setting up your OSC to output the instruction clock (fosc/4) on one of the PIC pins.