One of the most common errors we find in our student´s programming work is to put peripheral initialising code in the main loop, or in a routine (whether ISR or not) that accesses the peripheral. For example, TMOD= 0x11, in an ISR that only requires to reload TH0 anfd TL0.

We advice the students to put all the initialisations in a block at the beginning of the program, if possible. If there is a real need to change the configuration in other part of the program, think about the process carefully, including any special situation and side effects.

Is the LCD initialised only once?.

Alfredo del Rio.