st62t18c STMicroelectronics, st62t18c Datasheet - Page 12

• Manufacturer Part Number: st62t18c
• Description: 8-bit Mcus With A/d Converter, Auto-reload Timer, Uart, Osg, Safe Reset And 20-pin Package
• Manufacturer: STMicroelectronics

ST62T18C/E18C
MEMORY MAP (Cont’d)
1.3.6 Data RAM Bank Register (DRBR)
Address: CBh — Write only
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.
Bit 2.0 These bits are not used.
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.
The DRBR register can be addressed like a RAM
Data Space location at the address CBh; never-
theless it is a write only register that cannot be ac-
cessed with single-bit operations. This register is
used to select the desired 64-byte RAM bank of
the Data Space. The number of banks has to be
loaded 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).
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
12/82
12
7
-
-
-
DRBR4 DRBR3
-
-
0
-
the Data Space description for additional informa-
tion. The DRBR register is not modified when an
interrupt or a subroutine occurs.
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.
In DRBR Register, only 1 bit must be set. Other-
wise two or more pages are enabled in parallel,
producing errors.
Table 5. Data RAM Bank Register Set-up
DRBR
other
00h
01h
02h
08h
10h
ST62T18C/E18C
RAM Page 1
RAM Page 2
Reserved
Reserved
Reserved
None