I have a product dating from the late 1990s using the 68HC11E0CFNE2 processor that has started to experience a very high drop-out rate in production. Swapping the processor for an identical device from another batch fixes the problem.
The processor is used in expanded mode (external EPROM and RAM). I’ve put a logic analyser on the bus and soon after reset I can see the processor put out the 0xFFFE and 0xFFFF reset vector and the EPROM responds with the correct address (0xFECD) but the processor jumps to 0xE000 and starts executing the code there.
Probing around with a scope shows no obvious problems – signal quality and timing look fine (setup & hold of the reset vector wrt ‘E’ falling are 250ns and 70ns respectively).
The problem parts have MC68HC11E0CFNE2, 0M28Z, QQKZ1610A written on the package. Swapping those for parts with QQGP1342, QQHY1423 & QQJU1440D in the last line fixes the problem.
Any help would be very much appreciated!