ST6200C/ST6201C/ST6203C
MEMORY MAP (Cont’d)
3.1.6 Data ROM Window
3.1.6.1 Data ROM Window Register (DRWR)
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.
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.
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.
Address: 0C9h
— Write Only
and so on...
Reset Value = xxh (undefined)
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).
7
0
-
-
DRWR5 DRWR4 DRWR3 DRWR2 DRWR1 DRWR0
Figure 5. Data ROM Window
Bits 6, 7 = Not used.
PROGRAM
DATA SPACE
SPACE
0000h
000h
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.
040h
07Fh
Caution: This register is undefined on reset, it is
write-only, therefore do not read it nor access it us-
ing single-bit instructions (SET, RES...).
DATA ROM
WINDOW
64-BYTE
ROM
0FFFh
0FFh
12/104
1
ETC [ ETC ]
