9/14

ADDRESSING UP TO 4 MBYTES OF EXTERNAL MEMORY

Figure 9. Accessing almost 2M with the ST90R158

It is possible to increase the amount of accessible memory by reducing the size of the static

would increase the complexity of the hardware and software.

AS

DS

R/W

VCC

74HC573

ST90R158

EXTERNAL MEMORY

21-bit address

8-bit data

G

R/W (RAM and Flash only)

LE

74HC04

E

32 Kbytes

Seg 0

Seg 2

Seg 3

Seg 3F

EXTERNAL MEMORY

15-bit address

8 bit data

A[0..14]

E

A[15]

2 Mbytes

Seg 0

Seg 1

P0[0..7]

P1[0..7]

P2[0..7]

A[0..7]

A[8..15]

A[16..21]

A[0..21]

74HC04

0x00 0000

0x00 8000

0x01 0000

0x01 8000

32k

32k

32k

32k

32k

A[15]