LPC932problems

[Robert Dugour]

I want to let all LPC932 users know that we had to stand serious troubles using the Philips LPC932 series controllers.

Problem 1
Up to the F series (see errata sheet philips ) the handling of nested interrupts doesn't function correct.
So only buy series G or later controllers.
Problem 2
If there are uncertain startup conditions (as there are many in the field) the 932's pointer can startup with random content and thus damage the content of the (flash) program memory!!! The chip will start up with changed code or dont even start-up again.
Problem 3
The reset pin can be used as inputpin. However during start-up the resetpin is reset anyway for a short period. Leaving the pin open or connected to an,  at start-up uncertain, condition will cause a bad reset.
The chip doesn't start or starts with unexpected RAM content!!!
REMEDY  
1. If you want to use the 932 anyway be sure to have a very good conditioned power up and down circuitry that switches off directly and completely if there is a powerfail and switches on several milliseconds after power-on. In the off state  the suspply voltage should be less than 0,1V.
2. Don't use the reset pin as input but connect it to a reset circuitry.
Problem 4
The LPC 935 is not 5Volt compatable.
First P3.0 P3.1 and P1.5 are not 5 Volt compatable but thats in the datasheets.
Second the LPC932 can handle 5 volt only in special  powersupply conditions and only in OPENDRAIN mode.
This can cause serious trouble when you work with standard powersupplies or powersupplies that has different turnon and off times!
With standard powersupplies the switch on spikes of the 5 volt supply will damage the inputs of the 932 simply because they are above 5 Volt.
the result is a unexpected controller failures after several start-ups.
With different turn on and off times It can be that the controller input "sees" 5 VDC while the controller supply is still below working conditions. The rush-back current can damage the 932 inputs.
REMEDY
Dont use the 932 in mixed powersupply environment.
Or if you have to do secure  the 5VDC supply against spikes with a fast transil and use fets like the 2N7000 to isolate the 932 pins from the 5V environment.
Till now we had no problem with I2C pins but all other pins once in a while caused a damaged controller without these conditions.
Break detection method
lAst advice
If You use the break detect method be sure that no unexpected breaks can cause the controller to switch to program mode ats tsrat up.

These problems did cause us lots of troubles, incuding nights of working over , resoldering a few hundred F series controllers and adapting PCB's with transils and fet's
To save other engineers these sad experiences please send this email to al your LPC932 users.

Best regards
Robert Dugour
DEA engineering
Holland

[zhjun]

Thank very much!