Need advice for creating nS time delay

[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...

[Darrel Taylor]

This won't help Sayzer, but it's another example of why NOT to say RTFD all the time.

I was looking at the timing of a 628A. Trying to see if there was something that might work.
Looked at the capacitor discharge idea using a on-board comparator. But the response time was up to 600ns.
Hmmm, didn't expect them to be that slow.

Then was looking farther and came across this ...
Apparently, you can run a 16F628A at 4Ghz.
A 1ns delay would just be a NOP.

[skimask]

??????????
http://www.picbasic.co.uk/forum/atta...5&d=1197319528

[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.