This high-speed, 16-bit microcontroller is seamlessly designed to mirror the programming model of the iconic M68HC11 CPU. Notably, the HCS12 instruction set gracefully extends beyond the M68HC11’s capabilities, ensuring compatibility by flawlessly accommodating its source code without any alterations. Let’s delve into the intricacies of the HCS12.
Key Features of the HCS12:
Superior Data Handling: Boasting full 16-bit data paths, the HCS12 excels in efficiently conducting arithmetic operations and facilitating rapid mathematical computations.
ROM Space Efficiency: The HCS12’s adeptness in supporting instructions with odd byte counts, including a myriad of single-byte instructions, guarantees optimal ROM utilization.
Instantaneous Instruction Access: An innovative instruction queue ensures the HCS12 always has immediate access to at least three bytes of machine code at the beginning of every instruction.
Diverse Indexed Addressing Capabilities: The HCS12 offers a plethora of indexed addressing features, encompassing functionalities like using the stack pointer in all indexed tasks and accommodating accumulator offsets.
Programming Model:
Echoing the structure of the M68HC11 CPU, the HCS12’s programming model is characterized by two 8-bit general-purpose accumulators (A and B). These can be seamlessly merged into a singular 16-bit accumulator (D) for specific functions. Moreover, the HCS12 incorporates:
Two index registers (X and Y)
A 16-bit stack pointer (SP)
A 16-bit program counter (PC)
An 8-bit condition code register (CCR)
Data Types and Their Implementation:
The HCS12 is proficient in handling a diverse range of data types, from bits and binary-coded decimal numbers to various signed and unsigned integers.
It’s noteworthy that negative integers adopt the twoβs complement form. The HCS12 also introduces specialized five-bit and nine-bit signed integers solely for indexed addressing mode offsets.
Addressing in the HCS12:
One of the defining attributes of the HCS12 is its expansive 64-Kbyte standard address space, accommodating both 8-bit and 16-bit values.
Furthermore, 32-bit values are stored as four sequential bytes, with the highest byte occupying the initial address, without necessitating even boundary alignment.
The HCS12 also elegantly integrates all input/output (I/O) and intrinsic peripherals via memory mapping. This eliminates the need for specialized instruction syntax when accessing these addresses. Inherently, on-chip registers and memory are typically organized into blocks, offering the flexibility of relocation within the standard 64-Kbyte address space.
The HCS12 CPU has two 8-bit general-purpose accumulators (A and B) that can be concatenated into a single 16-bit
accumulator (D) for certain instructions. It also has:
β’ Two index registers (X and Y)
β’ 16-bit stack pointer (SP)
β’ 16-bit program counter (PC)
β’ 8-bit condition code register (CCR)
The CPU12 uses these types of data:
β’ Bits
β’ 5-bit signed integers
β’ 8-bit signed and unsigned integers
β’ 8-bit, 2-digit binary-coded decimal numbers
β’ 9-bit signed integers
β’ 16-bit signed and unsigned integers
β’ 16-bit effective addresses
β’ 32-bit signed and unsigned integers
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An Article by: Yashwanth Naidu Tikkisetty
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