X68C75 Datasheet, PDF (15/26 Pages) Xicor Inc. – Port Expander and E2 Memory

X68C75 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 X88C64, which interfaces to a multi-
plexed bus and takes an active LOW CE input. Example
3 maps the X88C64 to the bottom 8K program memory
space in the range of 0000-1FFFH. This approach
provides a total of 16K-bytes of program memory. Using
the same approach, two additional X88C64 devices can
be added and A13-A14 can be used as their CE inputs,
for a 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 X68C75 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 associ-
ated E² memory location are not available.
Figure 16. Example 3
68HC11
X68C75
A[15:8]
AD[7:0]
AS
R/W
E
PA
STRA
PB
STRB
VCC
AS
R/W
E
VCC
CE RESET
X88C64
AD7:0
A15:8
RD
ALE
R/W
A/D7-A/D0
A12-A8
A15 _CE
PSEN
2899 ILL F18
Figure 17. Example 4
68HC11
A[15:8]
AD[7:0]
STRA
PA
AS
AS STRB
R/W
R/W
PB
E
E
VCC
CE
15
128 I/O
2899 ILL F19