CD00001237 datasheet(13/105 Pages) STMICROELECTRONICS

13 / 105 page

ST6215C ST6225C

13/105

MEMORY MAP (Cont’d)

3.1.6 Data ROM Window Mechanism

The Data read-only memory window is located

from address 0040h to address 007Fh in Data

space. It allows direct reading of 64 consecutive

bytes located anywhere in program memory, be-

tween address 0000h and 0FFFh.

There are 64 blocks of 64 bytes in a 4K device:

– Block 0 is related to the address range 0000h to

003Fh.

– Block 1 is related to the address range 0040h to

007Fh.

and so on...

All the program memory can therefore be used to

store either instructions or read-only data. The

Data ROM window can be moved in steps of 64

bytes along the program memory by writing the

appropriate code in the Data ROM Window Regis-

ter (DRWR).

Figure 5. Data ROM Window

3.1.6.1 Data ROM Window Register (DRWR)

The DRWR can be addressed like any RAM loca-

tion in the Data Space.

This register is used to select the 64-byte block of

program memory to be read in the Data ROM win-

dow (from address 40h to address 7Fh in Data

space). The DRWR register is not cleared on re-

set, therefore it must be written to before access-

ing the Data read-only memory window area for

the first time.

Address: 0C9h

—

Write Only

Reset Value = xxh (undefined)

Bits 7:6 = Reserved, must be cleared.

Bits 5:0 = DRWR[5:0] Data read-only memory

Window Register Bits. These are the Data read-

only memory Window bits that correspond to the

upper bits of the data read-only memory space.

Caution: This register is undefined on reset, it is

write-only, therefore do not read it nor access it us-

ing Read-Modify-Write instructions (SET, RES,

INC and DEC).

0000h

0FFFh

000h

040h

07Fh

0FFh

DATA ROM

WINDOW

DATA SPACE

64-BYTE

ROM

PROGRAM

SPACE

DRWR5 DRWR4 DRWR3 DRWR2 DRWR1 DRWR0

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