Need advice for creating nS time delay

[sayzer]

At 4Mhz and at 20Mhz, how do we create a time delay for 200nS or 300nS?

Clever ideas?

[Acetronics2]

Hi, Sayzer

How are you ???

let's see ...

@ 20 Mhz ... a NOP is ... 1/ 5 Mhz = 200 ns ...

so, just insert, in your PbP program :

@ NOP ... and you get a 200 ns delay ...

You can try to Boost a 16F PIC @ 30 Mhz ... ( I've read about 32 Mhz ...)


With 18F series @ 40 Mhz , you will get 100 ns per NOP ... and it is a PbP DEFINE OSC ...

so, 2 or 3 NOP's will do it !

regards

Alain

PS : No PIC solution @ 4Mhz ( minimum instruction time is 1µs ... )

But you can play with external logic gates ( if possible ...) and use their propagation time : time can easily fall to 10 nS ...

[sayzer]

Thanks Alain.

I was playing with that calculation but I made it wrong.
Actually, jumping from one line to another is also around 200nS ~ 300nS at 20Mhz.
Just do A = B and get this delay.

But I am unable to use 20Mhz, so I must find another way of getting at least 300nS at 4Mhz.

[mister_e]

a single instruction @4Mhz is 1uSec, this will be impossible to be faster for this frequency.

[Acetronics2]

Hi, Sayzer

Depends on the Pic you want to use ... but, if an internal oscillator could be used ( 16F88 i.e. ) ...

you could think to change the osc. frequ by soft !!! ( 8Mhz maxi gives 500 ns ...)

but depends if you could "boost" your osc frequ. for some instructions ...

see 16F88 ( i.e.) datasheet $ 4.6.2 for further infos ...

Alain

[mister_e]

or... eh eh, a 18F and enable/disable the internal PLL on the fly...

[sayzer]

...
...you can play with external logic gates ( if possible ...) and use their propagation time : time can easily fall to 10 nS ...

a single instruction @4Mhz is 1uSec, this will be impossible to be faster for this frequency.

I was thinking to charge a 10pF capacitor and wait for its discharge.
But before spending hours on its tests, should I keep thinking on this?
Don't we have a cap on our input pins already? that is another issue.