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PDF AN1218 Data sheet ( Hoja de datos )
| Número de pieza | AN1218 | |
| Descripción | HC05 to HC08 Optimization | |
| Fabricantes | Freescale Semiconductor | |
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AN1218
HC05 to HC08 Optimization
By Mark Glenewinkel
CSIC Applications
Austin, Texas
Introduction
Freescale's HC05 Family of microcontrollers contains the world's most
popular 8-bit microcontroller units (MCUs). In keeping pace with
technology and the changing needs of the customer, Freescale has
designed the HC08 Family of MCUs. The HC08 Family CPU is a
performance extension to the HC05 Family of low cost MCUs. This
application note will describe the differences and advantages of the
HC08 Family CPU: the CPU08.
CPU08 is fully opcode and object code compatible with the HC05 CPU.
Any HC05 code will execute directly on the HC08 without instruction set
differences. As this application note will show, there are many
improvements to the speed and capability in the CPU08.
CPU08 is a faster processor. The basic execution speed of the CPU08
has been increased with advanced high performance CMOS
technology. Execution cycles of most instructions have been improved
with an advanced computer architecture.
CPU08 has more programming capability. It has more addressing
modes, better math support, and much improved data manipulation,
accessing, and moving capabilities. Looping and branching instructions
have also been optimized.
© Freescale Semiconductor, Inc., 2004. All rights reserved.
AN1218 Rev. 2
For More Information On This Product,
Go to: www.freescale.com
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Application Note
CPU05/CPU08 Programmer's Model Comparison
Table 1. Addressing Mode Comparison Table
Addressing Mode
Inherent
Immediate
Direct
Extended
Indexed, no offset
Indexed, 8-bit offset
Indexed, 16-bit offset
Relative
Stack Pointer, 8-bit offset
Stack Pointer, 16-bit offset
Memory to memory (4 modes)
Indexed w/post increment
Indexed, 8-bit offset, w/post increment
HC05
X
X
X
X
X
X
X
X
HC08
X
X
X
X
X
X
X
X
X
X
X
X
X
HC05 and HC08
Addressing Modes
Inherent instructions such as reset stack pointer (RSP) and multiply
(MUL) have no operand. Inherent instructions require no memory
address and are one byte long.
Immediate instructions contain a value that is used in an operation with
the index register or accumulator. Immediate instructions require no
memory address and are two bytes long. The operand is found in the
byte immediately following the opcode.
Direct instructions can access any of the first 256 memory addresses
with only two bytes. The first byte contains the opcode followed by the
low byte of the operand address. The CPU automatically uses $00 for
the high byte of the operand address. Most direct instructions are two
bytes long.
AN1218 Rev. 2
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Application Note
Index Registers
LDHX
STHX
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.
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.
AN1218 Rev. 2
For More Information On This Product,
Go to: www.freescale.com
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