8279 provides a 16 byte display memory and refresh logic. Every address in the display memory corresponds to a display unit with address zero representing the leftmost display unit. Output is accomplished by 8279 again and again sending out characters over the lines OUT A3-A0 and OUT B3-B0 and unit chooses address is over SL3-SL0.
For the auto increment left entry, after every writes to the display the addresses incremented by 1, so that the next character appears in the display unit to the right. Auto increment right entry let character to be displayed in electronic calculators form. It is reason for the display to be shifted left to 1 character and stores the next character from the right.