FXTH870xD
Sensors
52
Freescale Semiconductor, Inc.
8
Central Processing Unit
8.1
Introduction
This section provides summary information about the registers, addressing modes, and instruction set of the CPU of the HCS08
Family. For a more detailed discussion, refer to the
HCS08 Family Reference Manual, volume 1,
Freescale Semiconductor
document order number HCS08RMV1/D.
The HCS08 CPU is fully source- and object-code-compatible with the M68HC08 CPU. Several instructions and enhanced
addressing modes were added to improve C compiler efficiency and to support a new BACKGROUND DEBUG system which
replaces the monitor mode of earlier M68HC08 microcontrollers (MCU).
8.2
Features
Features of the HCS08 CPU include:
•
Object code fully upward-compatible with M68HC05 and M68HC08 Families
•
All registers and memory are mapped to a single 64-Kbyte address space
•
16-bit stack pointer (any size stack anywhere in 64-Kbyte address space)
•
16-bit index register (H:X) with powerful indexed addressing modes
•
8-bit accumulator (A)
•
Many instructions treat X as a second general-purpose 8-bit register
•
Seven addressing modes:
—
Inherent — Operands in internal registers
—
Relative — 8-bit signed offset to branch destination
—
Immediate — Operand in next object code byte(s)
—
Direct — Operand in memory at 0x0000–0x00FF
—
Extended — Operand anywhere in 64-Kbyte address space
—
Indexed relative to H:X — Five submodes including auto-increment
—
Indexed relative to SP — Improves C efficiency dramatically
•
Memory-to-memory data move instructions with four address mode combinations
•
Overflow, half-carry, negative, zero, and carry condition codes support conditional branching on the results of signed,
unsigned, and binary-coded decimal (BCD) operations
•
Efficient bit manipulation instructions
•
Fast 8-bit by 8-bit multiply and 16-bit by 8-bit divide instructions
•
STOP and WAIT instructions to invoke low-power operating modes
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