ST6208C datasheet(13/104 Pages) STMICROELECTRONICS

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ST6208C/ST6209C/ST6210C/ST6220C

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MEMORY MAP (Cont’d)

3.1.6 Data ROM Window

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.

Bit 5:0 = DRWR[5:0]

Data read-only memory Win-

dow 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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