The 44780 spec requires that the data (RS, RW, D4-D7) be placed on the bus some amount of time before raising the EN line. I seem to remember 40ns. If the '541 is driving the 6 lines all at once then you are loading the lines virtually simultaneously and ignoring the 40ns required address setup time.

You may be able to solve this problem by first having the '541 send out the data with the E line low and then send out the same data with the LCD's EN line high. That should give the 44780 the 40ns it requires.



I believe this is consistent with the problem I described above. Sometimes you get lucky and the 44780 is able to handle the data at the same instant that EN is pulsed and sometimes you don't get lucky. When you get lucky it works and when you don't get lucky it doesn't work.

Regards,
Craig Steiner