VRS51x570/580
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page 9 of 49
Data Bank Control Register
The DBANK register allows the user to enable the Data
Bank Select function and map the entire content of the
RAM memory in the range of 40h to 7Fh for
applications that would require direct addressing of the
expanded RAM content.
The Data Bank Select function is activated by setting
the Data Bank Select enable bit (DBANKSE) to 1
(setting this bit to zero disables this function). The four
least significant bits of this register control the mapping
of the entire 1K Byte on-chip RAM space into the 40h-
7Fh range.
TABLE 9: DATA BANK CONTROL REGISTER (DBANK) – SFR 86H
7
6
5
4
3
2
1
0
DBANKE
Unused
DBK3
DBK2
DBK1
DBK0
Bit
Mnemonic
Description
7
DBANKSE
Data Bank Select Enable Bit
DBANKE=1, Data Bank Select enabled
DBANKE=0, Data Bank Select disabled
6
Unused
-
5
Unused
-
4
Unused
-
3
DBK3
2
DBK2
1
DBK1
0
DBK0
Allows the mapping of the 1K RAM into
the 040h - 07Fh RAM space.
Windowed access to all the 1KB on-chip RAM in the
range of 40h-7Fh is described in the following table.
TABLE 10: BANK MAPPING DIRECT ADDRESSING MODE
DBK3
DBK2
DBK1
BSO
040h~07fh
mapping
address
Note
0
0
0
0
000h-03Fh
Lower 128 bytes
RAM
0
0
0
1
040h-07Fh
Lower 128 bytes
RAM
0
0
1
0
080h-0BFh
Upper 128 bytes
RAM
0
0
1
1
0C0h-0FFh
Upper 128 bytes
RAM
0
1
0
0
0000h-003Fh
On-chip externally
mapped 768 bytes
RAM
0
1
0
1
0040h-007Fh
On-chip externally
mapped 768 bytes
RAM
0
1
1
0
0080h-00BFh
On-chip externally
mapped 768 bytes
RAM
0
1
1
1
00C0h-00FFh
On-chip externally
mapped 768 bytes
RAM
1
0
0
0
0100h-013Fh
On-chip externally
mapped 768 bytes
RAM
1
0
0
1
0140h-017Fh
On-chip externally
mapped 768 bytes
RAM
1
0
1
0
0180h-01BFh
On-chip externally
mapped 768 bytes
RAM
1
0
1
1
01C0h-01FFh
On-chip externally
mapped 768 bytes
RAM
1
1
0
0
0200h-023Fh
On-chip externally
mapped 768 bytes
RAM
1
1
0
1
0240h-027Fh
On-chip externally
mapped 768 bytes
RAM
1
1
1
0
0280h-02BFh
On-chip externally
mapped 768 bytes
RAM
1
1
1
1
02C0h-02FFh
On-chip externally
mapped 768 bytes
RAM
Example: User writes #55h to 203h address:
MOV
DBANK, #8CH
;Set
bank
mapping
40h-07Fh
to
;0200h-023Fh
MOV
A, #55H
;Store #55H to A
MOV
43H, A
;Write #55H to 0203h
;address
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