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S3C9454B/F9454B
ADDRESSING MODES
3-7
INDEXED ADDRESSING MODE (X)
Indexed (X) addressing mode adds an offset value to a base address during instruction execution in order to
calculate the effective operand address (see Figure 3-7). You can use Indexed addressing mode to access
locations in the internal register file or in external memory.
In short offset Indexed addressing mode, the 8-bit displacement is treated as a signed integer in the range
– 128 to + 127. This applies to external memory accesses only (see Figure 3-8).
For register file addressing, an 8-bit base address provided by the instruction is added to an 8-bit offset contained
in a working register. For external memory accesses, the base address is stored in the working register pair
designated in the instruction. The 8-bit or 16-bit offset given in the instruction is then added to the base address
(see Figure 3-9).
The only instruction that supports Indexed addressing mode for the internal register file is the Load instruction
(LD). The LDC and LDE instructions support Indexed addressing mode for internal program memory, external
program memory, and for external data memory, when implemented.
dst
OPCODE
Two-Operand
Instruction
Example
Point to one of the
working register
(1 of 16)
Sample Instruction:
LD R0, #BASE[R1]
; Where BASE is an 8-bit immediate value
Program Memory
Register File
4 LSBs
Value used in
instruction
OPERAND
INDEX
X (OFFSET)
+
src
~
~
~
~
Figure 3-7. Indexed Addressing to Register File
Содержание S3C9454B
Страница 1: ...S3C9454B F9454B 8 BIT CMOS MICROCONTROLLER USER S MANUAL Revision 1 ...
Страница 25: ...PRODUCT OVERVIEW S3C9454B F9454B 1 10 NOTES ...
Страница 35: ...ADDRESS SPACES S3C9454B F9454B 2 10 NOTES ...
Страница 65: ...CONTROL REGISTERS S3C9454B F9454B 4 18 NOTES ...
Страница 123: ...CLOCK CIRCUIT S3C9454B F9454B 7 4 NOTES ...
Страница 133: ...RESET and POWER DOWN S39454B F9454B 8 10 NOTES ...
Страница 145: ...I O PORTS S3C9454B F9454B 9 12 NOTES ...
Страница 173: ...A D CONVERTER S3C9454B F9454B 12 8 NOTES ...
Страница 183: ...ELECTRICAL DATA S3C9454B F9454B 13 10 NOTES ...
Страница 193: ...S3F9454B MTP S3C9454B F9454B 15 4 NOTES ...