
2-14
MSM66577 Family User's Manual
Chapter 2 CPU Architecture
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Local register setting area
The local register setting area is the 2KB area of data memory from 0200H to 09FFH. Local
registers are set in 8-byte units, as specified by the lower 8 bits of LRB (LRBL).
Figure 2-6 shows the map of the local register setting area.
ER0
R0
R1
ER1
R2
R3
ER2
R4
R5
ER3
R6
R7
ER0
R0
R1
0200H
0208H
0A00H
R6
R7
LRBL =
00H
LRBL =
01H
LRBL =
FFH
ER3
Local register setting area:
Specified by 8 bits of LRBL,
in 8-byte units
0000H
0100H
0200H
0300H
0A00H
0FFFFFH
1200H
FIX area
Reserved area
SFR area
Internal
RAM area
External
data memory
area
Figure 2-6 Map of Local Register Setting Area
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External data memory area
The external data memory area is the 1,043,968-byte area of data memory from 1200H to
0FFFFFH (Note 1). If this external data memory is to be accessed, the secondary functions
of memory related pins (ports 0, 1, 2, 3 and 4) must be set. In a separate bus type, the
external data memory is accessed by Port 0 (data I/O: D0 to D7), Port 4 (address output:
A0 to A7), Port 1 (address output: A8 to A15), Port 2 (address output: A16 to A19), P3_3/
WR (write strobe output function) and P3_2/RD (read strobe output function) signals.
In a multiplexed bus type, the external data memory is accessed by Port 0 (combined I/O
of data input and address output: AD0 to AD7), Port 1 (address output: A8 to A15), Port
2 (address output: A16 to A19), P3_0/ALE (address latch enable output function), P3_2/
RD (read strobe output function) and P3_3/WR (write strobe output function) signals.
The 1,043,968-byte area from 1200H to 0FFFFFH of data memory is the external data
memory area. However, the ROM window function can be set by the ROM window setting
register. If the ROM window function is used in the specified area (address 1200H and
above), instead of accessing data in the data memory space, instructions (read operations)
will access data in the program memory space at the same address.
The ROM window function is valid if the register (ROMWIN) that enables the ROM window
function is set and the accessed (read) address is in external data memory.