Lpc2000

Hello everyone,

On 8 december 2005, Brendan Murphy posted a report where switching a
pin from GPIO to EINT (external interrupt) caused an edge-triggered
interrupt (message http://groups.yahoo.com/group/lpc2000/message/11212).

I replied to that message saying that we encountered precisely that
error on a single PCB out of 20 that we tested. Our hypothesis was
that the particular PCB had some kind of defect. This hypothesis was
based on the fact that the spurious interrupts _disappeared_ when
slightly bending the PCB.

We recently encountered a second board with exactly the same problem.
Here, too, pressure on the board influenced the occurrence of spurious
interrupts. Also similar was that the "pressure point" was on the
processor. In a related test, we heated the processor. This also
influenced the occurrence of the spurious interrupts.

We replaced the processor on the board (an LPC2138) by another one. No
more spurious interrupts occurred.

We are wondering whether this issue may perhaps be caused by the
processors not being handled correctly during manufacturing (perhaps
there was no baking before reflow soldering).

We have also tried to implement simple work-arounds, such as disabling
the external interrupt in the VIC before switching the pin from GPIO
to EINT, or clearing the interrupt in the VIC immediately after the
switch. Both these attempts failed.

I am reporting this to retract my earlier statement that the probable
cause is in the PCB or in the PCB design. In addition, I am curious
whether anyone can think of a work-around or fix for this issue.

Kind regards,
Thiadmer Riemersma