PULSIN - Logic Level Voltage Transiion

[dhouston]

Table 10.1 and Table 26.3 tell you what you need. You might also try measuring between rising edges to see if the period is what you think it is.

[cc1984]

Thanks Dave,
I will try your recommendations when I get to work tomorrow. Looking at the rise time 9 ns today makes me think that that is probably not the problem. Takes a lot of 9 nsec to add up to 3 usec I am going to look at it closely so at least I understand more about what is going on and the effects of rise/fall times in general. Looks like you have a bunch of stuff I need to look at on your web site. So much to do, so little time. Thanks, again. CC

[Acetronics2]

Hi, CC

@ First, you have to undersand how Pulsin works ...

1) input is set to an ... Input !
2) software counter is initialised and waits for the required edge to come ...
3) leading Edge detected ... the counter ... counts ( unbelievable, eh ? )
4) trailing edge detected ... counter stops counting ( see 3 )
5) counter value is transferred to the target variable.

from that ....

1) you need a little delay between the Pulsin command and the effective counting can start ( presetting delay )
2) you need a little delay between the counting is finished and a new command to be executed ...

after that ...

WHILE TRIGGER=1:WEND 'MAKE SURE I DON'T START IN THE MIDDLE OF A PULSE

is not useful ... as the pulsin command triggers ... on a level CHANGE ...

If measuring very short times ... your result will be either 3 or 4 ( example ) ... and precision will be VERY, VERY bad ...

So, ... it appears this way of measuring is " not so good " and you'd much better use the CCP module,in capture mode, with the 1/16 predivisor ... or if more samples required, a CD 4520 as an external 1/100 divider.

AND ... YES, you've hit the Basic languages functions ( not only PBP ) limitations .... ... so, you have to directly drive the Pic registers !!!

Alain

[cc1984]

Alain,
Thanks you very much for the clear explaination of how the pulsin function works! I will investigate the CCP capture mode method.
Thanks, again.
CC