On the 8051 in a write it first it puts out A0-A7 and that is put into a 8 bit latch then it puts out the data on AD0-7 and the high address on to the buses.
The uC has 8 address bits output and one latch control, say E. An external 8-bit latch is mounted onto the address bus.
At first the latch control is LOW, and the lower 8 address bits are driven onto the address bus. A moment later, E goes HIGH and the latch "locks" its data permanently. Then, the uC can use the address bus to either display the 8 higher address bits, or use the bus to display data.