參數(shù)資料
型號: ST6218CB6/XXX
廠商: STMICROELECTRONICS
元件分類: 微控制器/微處理器
英文描述: 8-BIT, MROM, 8 MHz, MICROCONTROLLER, PDIP20
封裝: 0.300 INCH, PLASTIC, DIP-20
文件頁數(shù): 4/82頁
文件大小: 937K
代理商: ST6218CB6/XXX
Obsolete
Product(s)
- Obsolete
Product(s)
12/82
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
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
70
-
DRBR4 DRBR3
-
DRBR
ST62T18C/E18C
00h
None
01h
Reserved
02h
Reserved
08h
RAM Page 1
10h
RAM Page 2
other
Reserved
12
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