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ST9 EXTERNAL MEMORY INTERFACE CONFIGURATION

2.3 HARDWARE IMPLEMENTATION EXAMPLES

Depending on the mode configuration (and the availability for your device), the hardware im-

plementation can be different.

For a small memory model, you will have to use a latch connected to the multiplexed Address/

Data bus. The figure below shows an example of this (Figure 3).

Figure 3. Small Memory Model Example (For MC = 0)

For a ST9 microcontroller with the large External Memory Interface model, you can benefit

from the possibilities of the extended mode configuration.

The following figure shows an example of large memory model.

Figure 4. Large Memory Model example for MC = 1

RAM

64 Kbytes

G

E

A0-A15

A15-A8

ST9

DSN

P1

Q0-Q7

P0

W

RWN

D1-D8

ASN

OE

LE

Q1-Q8

A0-A7/D0-D7

LATCH

G

A0-A15

A15-A8

ST9

DSN

P1

Q0-Q7

P0

W

RWN

D1-D8

ALE

OE

LE

Q1-Q8

A0-A7/D0-D7

LATCH

P9

Comparator

E

Memory

4MB