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參數(shù)資料
| 型號： | AN1218 |
| 廠商： | 飛思卡爾半導體(中國)有限公司 |
| 英文描述： | HC05 to HC08 Optimization |
| 中文描述： | 以HC08的優(yōu)化HC05 |
| 文件頁數(shù)： | 11/56頁 |
| 文件大?。?/td> | 417K |
| 代理商： | AN1218 |
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Application Note
Index Registers
AN1218 Rev. 2
11
LDHX
Load 16-bit Index Register
Operation:
H:X
←
(M:M+1)
Description: Loads the contents of the speci ed memory
location into the 16-bit index register H:X.
The condition codes are set according to the
data.
STHX
Store 16-bit Index Register
Operation:
(M:M+1)
←
(H:X)
Description: Stores the 16-bit index register H:X to the
speci ed memor y location. The condition
codes are set according to the data.
Software
Techniques Using
Indexed
Addressing, Tables
The CPU08 index register has some distinct advantages over the
CPU05 index register. Even though the CPU05 has 16-bit index offset,
the 8-bit index register restricts indexing to a maximum of 256 bytes.
CPU08 with its H register extension allows full 16-bit index addressing
equaling 65,536 bytes of memory access. Proper 16-bit pointers allow
efficient compiling of C code and other higher level languages.
Maximum table lengths in the CPU08 which can be accessed in a single
instruction are therefore 64 KByte. An optional address extension
module can extend the data space beyond 64 KBytes, but the maximum
offset remains 64 KBytes. Index addressing modes include 8- and 16-
bit offsets.
Many programmers like to use calculated addressing. CPU08 has a
new instruction, AIX, that allows the addition of a two's complement
number. Table access is easier and more flexible.
The H:X index register can also be used as an auxiliary 16-bit
accumulator. Sixteen-bit data comparisons are easier with the CPHX
instruction.
The following section illustrates the advantage of using a 16-bit index
register.
F
Freescale Semiconductor, Inc.
For More Information On This Product,
Go to: www.freescale.com
n
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