X88C75 Datasheet, PDF (15/27 Pages) Xicor Inc. – Port Expander and E2 Memory

X88C75 SLIC^® E²
Example 3
If an application requires larger program memory stor-
age and both extra ports, then example 2 does not meet
this requirement. Since the LAM feature uses port B to
output the non-multiplexed address, then port B cannot
be also used as general purpose I/O. The solution to this
problem is to use X68C64, which interfaces to a multi-
plexed bus and takes an active HIGH CE input. Example
3 maps the X68C64 to the top 8K program memory
space in the range of 8000-FFFFH. This approach
provides a total of 16K-bytes of program memory. Using
the same approach, two additional X68C64 device can
be added and A13-A14 can be used as their CE inputs,
for the total of 32K-bytes of program memory. Ports A
and B are still available to handle any general purpose
I/O functions.
Example 4
For those applications using extensive I/O, up to 128
I/O pins are obtained by placing 8 of the X88C75 devices
on the same bus. This approach gives a total of 64K-
bytes of program memory space, and 128 I/O pins. Note
that the SFRM can overlap the E²M address space,
however, only the SFR resources are accessible and
the associated E² memory location are not available.
Figure 16. Example 3
8051
A15:8
AD7:0
ALE
WR
RD
PSEN
EA
X88C75
PA
STRA
PB
STRB
ALE
WR
RD
PSEN
CE RESET
A15
AD7:0
A15:8
X68C64
CE
E
AS
SEL
WR
A/D7-A/D0
A12-A8
2887 ILL F20
Figure 17. Example 4
8051
A15:8
AD7:0
ALE
WR
RD
PSEN
EA
STRA
PA
ALE STRB
WR
PB
RD
PSEN
CE RESET
15
128 I/O
2887 ILL F21