I migrated some software from AT89S8252 to 8253 (modify my OEM programmer, the less problematic thing). I found a series of bugs/new non-documenetd issues as:
- ALE misses one pulse on each MOVX instruction, even using internal EEPROM. AT89S8252 not (in fact any 8051)(I had to use another xtal for a PLL).
- Vcc rise time is critical (2ms max). Otherwise, internal clock become unstable (half the speed, for example). Not in AT89S8252.
- With little spikes in Vcc (500mVpp)(I know, they should not be there!) AND low temperature, the AT89S8253 is unable to read eeprom in the very beginning of software execution. Of course, AT89S8252 works perfectly.
- Previous "bug" eventually solved adding 10ms "dummy" delay after reset and before any EEPROM reading. Why, why??
All this things happen with last revision R chip.
Finally, I learned to live with this, and lukely, I could buy some pieces of old 8252.
Salud!