Here's a weird problem with an 87C51FA.I've programmed the chip with a simple problem that just toggle's all the ports from high to low over and over and just keeps looping back.
All interrupts are disabled. The chip has EA pulled high (external access disabled). This program has been tested on a nohau emulator and works just fine. But when the chip is powered up it just ignores the program and tries to access external memory. All pins are checked on a 'scope and ports P0 & P2, data and addressing lines show activity but no other port pins show any activity at all. PSEN and ALE is active indicated the unit thinks it's in external access mode. These are plastic OTP parts. To add to the mystery ceramic windowed parts do not show external access behavior under exactly the same conditions, but show no port activity either.
Does anybody out there no whats going on.