hi,
the easy way is use additional port (for example, P1) as most high address lines. As well you is able to make some ports` pins as chips` selectors. It is easy way with minimal external additional hardware. In hard cases, you should use PLD or MCU with PLD. For example, here we use T89C51CC01 together with 5+5 external input/output 8-bits ports, AMD 4Mbit AM29F040B flash chip, two Samsung 4Mbit K6T4008 RAMs, 1-wire Dallas chips, LCD, DIP-switches, PWM music, etc (=
All the hardware are accepted via Altera EPM chip, which has control and additional address registers inside. m/ wow! ((=
good days!