switched on. Then variable resistors P3 and P4 can be adjusted to the required shift in both horizontal and verti-
cal plane.
Construction
Make ready the single sided PCB which is not too
complex so it can be done in your home workshop.
After placing and soldering components check whe-
ther voltage regulators are functioning properly. If
yes, then adjust all variable resistors into middle posi-
tion and start with final adjustments.
Interface for serial ports
Operation
In case we are intended to use a serial port instead of
a parallel port we have to adjust voltage levels prop-
erly. For this task a well known circuit MAX232 can
be used. Since the change to a serial port we can save
some connections on the microprocessor. In this case
we can decide ourselves whether to utilize FLIP func-
tion (PORTB, 0-P9) and for adjusting the necessary
shift it is enough to take a short circuit to the right
place (PORTC, 4-P7). Beside these, we can test com-
munications between PC and interface if we put the
