Many microcontrollers share the same pins to output the lower address and transfer data. In order to hold the address constant while the data are transferred, the address information is stored in a latch which is enabled by the control signal ALE (address latch enable) as shown in Figure 5-97. Connect this latch to the microcontroller such that it takes what is on the lower address and data lines while ALE is HIGH and holds it on the lower address only lines when ALE is LOW.

Figure 5-97

A15 A14 A13 A12 A11 A10 A9 A8 ALE AD7 AD6 AD5 AD4 AD3 AD2 AD1 ADO |||||| |||||| Upper address only 68888858 EN 82882889 Lower address only Shared low address and data 16-bit address 8-bit data