st62t62b STMicroelectronics, st62t62b Datasheet - Page 9

• Manufacturer Part Number: st62t62b
• Description: 8-bit Otp/eprom Mcus With A/d Converter, Auto-reload Timer And Eeprom
• Manufacturer: STMicroelectronics

MEMORY MAP (Cont’d)
1.3.5 Data Window Register (DWR)
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 (top memory ad-
dress depends on the specific device). All the pro-
gram memory can therefore be used to store either
instructions or read-only data. Indeed, the window
can be moved in steps of 64 bytes along the pro-
gram memory by writing the appropriate code in the
Data Window Register (DWR).
The DWR can be addressed like any RAM loca-
tion in the Data Space, it is however a write-only
register and therefore cannot be accessed using
single-bit operations. This register is used to posi-
tion the 64-byte read-only data window (from ad-
dress 40h to address 7Fh of the Data space) in
program memory in 64-byte steps. The effective
address of the byte to be read as data in program
memory is obtained by concatenating the 6 least
significant bits of the register address given in the
instruction (as least significant bits) and the con-
tent of the DWR register (as most significant bits),
as illustrated in
when addressing location 0040h of the Data
Space, with 0 loaded in the DWR register, the
physical location addressed in program memory is
00h. The DWR register is not cleared on reset,
therefore it must be written to prior to the first ac-
cess to the Data read-only memory window area.
Figure 5. Data read-only memory Window Memory Addressing
WINDOW REGISTER
ADDRESS:A19h
CONTENTS
DATA ROM
(DWR)
Example:
DWR=28h
ROM
Figure 5
13
7
below. For instance,
12
6
11
5
1
1
10
4
0
0
9
3
1
1
8
2
0
0
7
1
0
0
0
0
6
0
1
0
1
0
Data Window Register (DWR)
Address: 0C9h — Write Only
Bits 6, 7 = Not used.
Bit 5-0 = DWR5-DWR0: 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. Nei-
ther read nor single bit instructions may be used to
address this register.
Note: Care is required when handling the DWR
register as it is write only. For this reason, the
DWR contents should not be changed while exe-
cuting an interrupt service routine, as the service
routine cannot save and then restore the register’s
previous contents. If it is impossible to avoid writ-
ing to the DWR during the interrupt service rou-
tine, an image of the register must be saved in a
RAM location, and each time the program writes
to the DWR, it must also write to the image regis-
ter. The image register must be written first so
that, if an interrupt occurs between the two instruc-
tions, the DWR is not affected.
5
5
0
0
7
-
4
4
1
1
3
3
1
1
-
2
2
0
0
DWR5 DWR4 DWR3 DWR2 DWR1 DWR0
1
1
0
0
ST62T52B ST62T62B/E62B
0
0
1
1
PROGRAM SPACE ADDRESS
DATA SPACE ADDRESS
DATA SPACE ADDRESS
IN INSTRUCTION
40h-7Fh
READ
59h
VR01573C
:
:
0
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