Delay question

[mister_e]

Come on Skimask

[therian]

Can someone please explain me how to use assembly to make shorter delay than pauseus can make ?

[HenrikOlsson]

Hi,
The shortest possible delay is achieved by using the assembler command NOP (short for No OPeration):

@NOP       'Delay for OSC/4

The NOP instruction takes 1uS at 4Mhz and 250nS at 20Mhz etc. If you want longer delay add more NOP instructions or build a loop, but then it's probably easier to use PauseUs anyway.

/Henrik Olsson.

[therian]

thank you, as i understand 1us is minimum limit for 4mhz crystal

[HenrikOlsson]

Therian,
Yes, that is correct. With a 4Mhz X-tal one intruction cylce is 1uS and since the NOP command takes one cycle to execute the delay will be 1uS.

/Henrik Olsson.

[therian]

just curious, is 250nS enough to generate radio frequency directly from pic without any rf modules, it sound like cheap radio link

[HenrikOlsson]

Therian,
Well, let's see:

Start:
  PortB.1 = 1     'Set pin high        
@ NOP             'Wait....Two NOP's are neede if we want 50% dutycycle
@ NOP             'since the GOTO takes two instruction cylcles.
  PortB.1 = 0     'Set pin low
Goto Start        'Do it again. The GOTO takes the same time as two NOP's

This, I think, will generate a pulsetrain with 50% duty cycle. The frequency would be ~833kHz. Not much of a radio frequency.... besides that, you can't do anything else in the code without slowing it down more...much more.

/Henrik Olsson.