ST62T30B ST62E30B
MEMORY MAP (Cont’d)
1.3.6 Data RAM/EEPROM Bank Register
(DRBR)
This register is not cleared during the MCU initiali-
zation, therefore it must be written before the first
access to the Data Space bank region. Refer to
the Data Space description for additional informa-
tion. The DRBR register is not modified when an
interrupt or a subroutine occurs.
Address: CBh
—
Write only
7
0
-
-
-
DRBR4 DRBR3
-
DRBR1 DRBR0
Notes:
Care is required when handling the DRBR register
as it is write only. For this reason, it is not allowed
to change the DRBR contents while executing in-
terrupt service routine, as the service routine can-
not save and then restore its previous content. If it
is impossible to avoid the writing of this register in
interrupt service routine, an image of this register
must be saved in a RAM location, and each time
the program writes to DRBR it must write also to
the image register. The image register must be
written first, so if an interrupt occurs between the
two instructions the DRBR is not affected.
Bit 7-5 = These bits are not used
Bit 4 - DRBR4. This bit, when set, selects RAM
Page 2.
Bit 3 - DRBR3. This bit, when set, selects RAM
Page 1.
Bit2. This bit is not used.
Bit 1 - DRBR1. This bit, when set, selects
EEPROM Page 1.
Bit 0 - DRBR0. This bit, when set, selects
EEPROM Page 0.
In DRBR Register, only 1 bit must be set. Other-
wise two or more pages are enabled in parallel,
producing errors.
The selection of the bank is made by programming
the Data RAM Bank Switch register (DRBR regis-
ter) located at address CBh of the Data Space ac-
cording to Table 1. No more than one bank should
be set at a time.
Table 5. Data RAM Bank Register Set-up
DRBR
00
ST62T30B/E30B
None
The DRBR register can be addressed like a RAM
Data Space at the address CBh; nevertheless it is
a write only register that cannot be accessed with
single-bit operations. This register is used to select
the desired 64-byte RAM/EEPROM bank of the
Data Space. The number of banks has to be load-
ed in the DRBR register and the instruction has to
point to the selected location as if it was in bank 0
(from 00h address to 3Fh address).
01
EEPROM Page 0
EEPROM Page 1
RAM Page 1
RAM Page 2
Reserved
02
08
10h
other
12/86
28
STMICROELECTRONICS [ ST ]
