The circuit is attached. When the motor is not connected and only LED is connected to driver outputs of l293d, there are no issues. When I connect the motor, at the moment the power is supplied to it, the LCD displays in the first row white boxes instead of letters. The DC motor has obviously effect on the circuit as when it is connected and EN pin is turned off, one can see that the LED slowly dims as the DC generated back current. But I thought L293D should protect the rest of the circuit from those effects. Another thought is that somehow, to turn DC motor on the L293D needs to draw more power (why?) and this causes current drop in the LCD part of the circuit. Can anyone help out?
The wiring of the power barrel jack and L293D is incorrect.
The positive of the barrel jack must go to the positive rail of the breadboard. Pins 16 and 8 of the L293D should then connect to that power rail.
There is also the issue that the RTC has no power.