If the LCD is starting out oK working and then after a time goes to a state that just the upper line is filled with black blocks it sounds to me like the display is getting reset. Steve mentioned that the power to the LCD could be screwey.....but is also possible that the RESET signal to the LCD is not working the way it should be. You should not just leave the LCD RESET signal open at the 44780. Either tie it to a port pin or to the inactive level voltage.

If you already have this pin tied to a port pin then in all likelyhood the code that you have "that works perfectly" has a bug in it that makes it run away and accidently modifies the port pin that the RESET is connected to and causes the upset of the LCD module to occur.

Besides the issues related to an interrupt service routine (ISR) that Erik questioned you about I can think of several other things that may be related to your problem.

- Maybe you have not set your stack pointer (SP) in a safe place and stack usage is over writing some critical variables.

- Maybe you have mismatched pushes and pops in your program and some RET instruction is getting hosed becasue it does not access a valid return address on the stack.

- Maybe your project has a watchdog timer in it that is not being handled properly.


BTW.....it is very typical that programs to declared to be "perfect" are not so elegant after all.

Michael Karas