Lpc2000

On other microcontrollers I've used, it was possible to start a single 
timer on a rising edge, and capture-and-reset on a falling edge (to 
capture the pulse time).

It doesn't look like this method is available on the (for example) 
LPC2131. What would be a good mechanism for these microcontrollers? 
Start two timers, feed the PWM to two pins, have one capture-and-reset 
on rising edge, the other on the falling edge? (the difference between 
the two capture registers would be the pulse time) or is there a 
better way?

Thanks,
-Pete.

Peter,

use one Timer and capture on both edges.  Depending on your system
setup this limits the minimum pulse width somewhat but assuming it is
more than 1 usec it should be doeable.  You have to make sure that you
did already read the first value before the second got captured.
Another option is to use two capture inputs (not two timers) and do it
like you proposed the difference of the two timer snapshots.

hth Bob


--- In lpc2000@yahoogroups.com, "Peter Gray" <peter_f_gray@y...> wrote:

> 
> On other microcontrollers I've used, it was possible to start a single 
> timer on a rising edge, and capture-and-reset on a falling edge (to 
> capture the pulse time).
> 
> It doesn't look like this method is available on the (for example) 
> LPC2131. What would be a good mechanism for these microcontrollers? 
> Start two timers, feed the PWM to two pins, have one capture-and-reset 
> on rising edge, the other on the falling edge? (the difference between 
> the two capture registers would be the pulse time) or is there a 
> better way?
> 
> Thanks,
> -Pete.

Thanks Bob. Capturing both edges on a single timer works like a 
charm (I use a global var as a counter, and use it to populate a 
small global array from within the interrupt). By capturing three 
values, I can do some simple math to figure out which edge is which, 
and hence grab the pulse width.

-Pete.
--- In lpc2000@yahoogroups.com, "lpc2100_fan" <lpc2100_fan@y...> 
wrote:
> 
> Peter,
> 
> use one Timer and capture on both edges.  Depending on your system
> setup this limits the minimum pulse width somewhat but assuming it 
is
> more than 1 usec it should be doeable.  You have to make sure that 
you
> did already read the first value before the second got captured.
> Another option is to use two capture inputs (not two timers) and 
do it
> like you proposed the difference of the two timer snapshots.
> 
> hth Bob
> 
> 
> --- In lpc2000@yahoogroups.com, "Peter Gray" <peter_f_gray@y...> 
wrote:
> > 
> > On other microcontrollers I've used, it was possible to start a 
single 
> > timer on a rising edge, and capture-and-reset on a falling edge 
(to 
> > capture the pulse time).
> > 
> > It doesn't look like this method is available on the (for 
example) 
> > LPC2131. What would be a good mechanism for these 
microcontrollers? 
> > Start two timers, feed the PWM to two pins, have one capture-and-
reset 
> > on rising edge, the other on the falling edge? (the difference 
between 

> > the two capture registers would be the pulse time) or is there a 
> > better way?
> > 
> > Thanks,
> > -Pete.