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16-bit signed PC index
(sign extended to 20 bits)
Program
counter PC
20-bit signed add
Memory address
FFFFF
00000
Lo
wer 64 KB
0FFFF
10000
PC.19:0
Upper Memory
PC.19:16 > 0
16-bit byte index
1 ... 15
19
16 15
0
S
PC ±32 KB
S
xxxxh
Address
Space
F740h
4766h
PC
0103Ah
01038h
01036h
01038h
+0F740h
00778h
Before:
Address
Space
After:
05D0h
01034h
xxxxh
F740h
4766h
PC
0103Ah
01038h
01036h
50D0h
01034h
xxxxh
xx45h
0077Ah
00778h
xxxxh
xx77h
0077Ah
00778h
32h
+45h
77h
src
dst
Sum
01036h
+04766h
0579Ch
xxxxh
xx32h
0579Eh
0579Ch
xxxxh
xx32h
0579Eh
0579Ch
Addressing Modes
4.4.3.2
MSP430 Instruction With Symbolic Mode in Upper Memory
If the PC points to an address above the lower 64-KB memory, the PC bits 19:16 are used for the address
calculation of the operand. The operand may be located in memory in the range PC ± 32 KB, because the
index, X, is a signed 16-bit value. In this case, the address of the operand can overflow or underflow into
the lower 64-KB memory space as shown in
and
.
Figure 4-20. Symbolic Mode Running in Upper Memory
105
SLAU272C – May 2011 – Revised November 2013
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