Robert Bailey

MCF51JM Random ,extra output transition after input capture ISR,

Discussion created by Robert Bailey on Mar 22, 2012
Latest reply on Mar 25, 2012 by Robert Bailey

Using CW 6.3


I have an input capture,  capturing both edges of a square wave,  measuring the periods based on the delta of the timer capture,  in this ISR I toggle an output to drive some instrumentation.  I do it this way as I use the pin to encode other data in other modes.  What is happening is that at random times (every 10 to 20 seconds)  there will be an extra write to the pin,  changing its state an additional time.  This extra change of state happens AFTER the ISR completes.  It happens in either polarity,  i.e.  if the ISR sets the pin,  then every once in a while the pin will clear after the ISR returns,  and vice versa.


The input capture is TPM12,  the pin in question PTA5,  both of which are set up with Processor Expert beans/components.


If I toggle PTF5 in the same way,  this does not happen


but it DOES happen if I write to  PTB4 in the ISR,  although the stray pulse on PTA5 and PTB4  (when I write to both) doesn't occurr at the same time.


changing PTA5 to RGPIO cleared it up,  but PTB5 and PTF5 don't have RGPIO functionality.


It is truly bizarre.  Has any one else seen something like this!


I'm going to try to boil the project down to the minimum that exhibits this,  and get it to happen on the demo board.  Then perhaps put in an SR.  But I thought I'd toss it out to the audience first.