The AD0 - AD7 lines are used as lower order 8-bit address bus and data bus , in time division multiplexed manner .
The A8 - A15 lines are used for higher order 8-bit of address bus.
There are seven memory and I/O control lines -
RD : indicates a READ operation when the signal is LOW.
WR : indicates a WRITE operation when the signal is LOW.
: indicates memory access for LOW and I/O access for HIGH.
ALE : ALE is an Address Latch Enable signal, this signal is HIGH when address information is present in AD0-AD-7. The falling edge of ALU can be used to latch the address into an external buffer to de-multiples the address bus.