Connect:
--------

RAM:
RD- to RD-
WR- to WR-
D0..D7 to D0..D7
A0..A15 to A0..A15
A16 to Px.x1 (one free port line)
CS- to Px.x2 (another free port line)

DECODER: (i.e. one 74xx138)
A to A2
B to A3
C to A4
CS- to gnd
CS- to gnd
CS to Px.x2

8255':
A1,A2 to A1,A2
D0..D7 to D0..D7
RD- to RD-
WR- to WR-
CS- to each output of decoder


USE:
Px.x1 to select the upper or lower 64K RAM
Px.x2 to select I/O or RAM



Félix.