EF9345 datasheet(11/38 Pages) STMICROELECTRONICS

11 / 38 page

MEMORY ORGANIZATION

Logical And Physical Addressing

The physical 16-Kbyte addressingspace is logicaly

partitioned by EF9345 into 40-byte buffers (Fig-

ure 8). More precisely, a logical address is given by

an X, Y, Z triplet where :

- X = (0 to 39) points to a byte inside a buffer,

- Y = (0, 1 ; 8 to 31) points to a buffer inside a

1 Kbyte blocks,

- Z = (0 to 15) points to a block.

Obviously, 1 K = 2

10 = 1024 cannot be exactly

divided by 40. Consequently, any block holds 25

full buffers and a 24-byte remainder. Provided that

the physical memory is a multiple of 2 Kbytes, the

remainders are paired in such a way as to make

available :

- A full buffer (Y = 1) in each even block,

- A partial buffer (Y = 1 ; X = 32 to 39) in each odd

block.

DISTRICT

839

DISTRICT

BLOCK 0

(1Kbyte)

BLOCK 1

BLOCK 2

BLOCK 3

839

120-BYTE ROW BUFFER

80-BYTE ROW BUFFER

- Row buffers lay indide a district

- At two or three successive block addresses (modulo 4)

- First block address is even

Notes :

Figure 8 : Memory Row Buffer

Pointers

Each X, Y and Z component of a logical address is

binary encoded and packed in two 8-bits registers.

Such a register pair is a pointer (Figure 9). EF9345

contains two pointers :

- R4, R5 : auxiliary pointer,

- R6, R7 : main pointer.

R5 and R7 have the same format. Each one holds

an X component and the two LSB’s of a Z compo-

nent. This packing induces a partitioning of Z in 4

districts of 4 blocks each.

R5, R7 points to a block number in a district. R4

and R6 have a slightly different format : Each one

holds a Y component and the LSB of the district

number. But R6 holds both district MSB

Figure 11 gives the logical to physical address

transcoding scheme performed on chip.

d’1

3210

Y = (0, 1 ; 8 to 31)

3210

X= 0to 39

MAIN

POINTER

d’0

3210

Y’ = (0, 1 ; 8 to 31)

b’0

b’1

3210

X’ = 0 to 39

AUXILIARY

POINTER

210

Z = (0 to 15)

2= 0

4= 0

6= 0

3= 1

5= 1

7= 1

X incrementation

Modulo 40

Y incrementation

Modulo 24

Z incrementation/

decrementation

Modulo 4 on the

block number only

Figure 9 : Pointer Auto Incrementation

EF9345

11/38

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