Freescale 68HC12
Encyclopedia
The 68HC12 is a microcontroller
family from Freescale Semiconductor
with an 8-bit
ALU and 16-bit
linear addressing. Originally introduced in the mid 1990s, the architecture is an enhancement of the Freescale 68HC11
. Programs written for the HC11 are usually compatible with the HC12, which has a few extra instructions
. The first 68HC12 derivatives had a maximum bus speed of 8MHz and flash memory sizes up to 128 kB
.
accumulators A and B (referred to as a single 16-bit accumulator, D, when A & B are cascaded so as to allow for operations involving 16 bits), 2 16-bit registers X and Y, a 16-bit program counter, a 16-bit stack pointer and an 8 bit Condition Code Register.
The MC9S12NE64 was introduced by Freescale in September 2004, claiming to be the "industry's first single-chip fast-Ethernet Flash microcontroller." It features a 25 MHz HCS12 CPU, 64 kB of FLASH EEPROM, 8 kB of RAM, and an Ethernet 10/100 Mbit
/s controller.
Freescale announced the MC9S12XEP100 in May 2006 to further extend the S12X family to 50MHz bus speed and add a Memory protection
unit (based on segmentation
) and a hardware scheme to provide Emulated EEPROM
.
HCS12 products contain a single processor, the HCS12X feature the additional XGATE peripheral processor.
The XGATE co-processor is a 16-bit RISC processor operating at twice the main bus clock. It offloads work from the HC12 core by handling interrupts only and does not run a background loop. The first versions of the XGATE do not allow for higher priority interrupts to pre-empt a currently handled interrupt, but the "XGATEV3" as featured in the 9S12XEP100 does allow this. The HC12 can trigger software interrupts on the XGATE core. A semaphore system is implemented to allow the S12X and XGATE cores to share peripherals.
Microcontroller
A microcontroller is a small computer on a single integrated circuit containing a processor core, memory, and programmable input/output peripherals. Program memory in the form of NOR flash or OTP ROM is also often included on chip, as well as a typically small amount of RAM...
family from Freescale Semiconductor
Freescale Semiconductor
Freescale Semiconductor, Inc. is a producer and designer of embedded hardware, with 17 billion semiconductor chips in use around the world. The company focuses on the automotive, consumer, industrial and networking markets with its product portfolio including microprocessors, microcontrollers,...
with an 8-bit
8-bit
The first widely adopted 8-bit microprocessor was the Intel 8080, being used in many hobbyist computers of the late 1970s and early 1980s, often running the CP/M operating system. The Zilog Z80 and the Motorola 6800 were also used in similar computers...
ALU and 16-bit
16-bit
-16-bit architecture:The HP BPC, introduced in 1975, was the world's first 16-bit microprocessor. Prominent 16-bit processors include the PDP-11, Intel 8086, Intel 80286 and the WDC 65C816. The Intel 8088 was program-compatible with the Intel 8086, and was 16-bit in that its registers were 16...
linear addressing. Originally introduced in the mid 1990s, the architecture is an enhancement of the Freescale 68HC11
Freescale 68HC11
The 68HC11 is an 8-bit microcontroller family introduced by Motorola in 1985. Now produced by Freescale Semiconductor, it descended from the Motorola 6800 microprocessor. It is a CISC microcontroller...
. Programs written for the HC11 are usually compatible with the HC12, which has a few extra instructions
Instruction set
An instruction set, or instruction set architecture , is the part of the computer architecture related to programming, including the native data types, instructions, registers, addressing modes, memory architecture, interrupt and exception handling, and external I/O...
. The first 68HC12 derivatives had a maximum bus speed of 8MHz and flash memory sizes up to 128 kB
Kilobyte
The kilobyte is a multiple of the unit byte for digital information. Although the prefix kilo- means 1000, the term kilobyte and symbol KB have historically been used to refer to either 1024 bytes or 1000 bytes, dependent upon context, in the fields of computer science and information...
.
Architecture of the 68HC12
Like the 68HC11, the 68HC12 has 2 8-bitBit
A bit is the basic unit of information in computing and telecommunications; it is the amount of information stored by a digital device or other physical system that exists in one of two possible distinct states...
accumulators A and B (referred to as a single 16-bit accumulator, D, when A & B are cascaded so as to allow for operations involving 16 bits), 2 16-bit registers X and Y, a 16-bit program counter, a 16-bit stack pointer and an 8 bit Condition Code Register.
HCS12/MC9S12 derivatives
Beginning in 2000 the family was extended with the introduction of the MC9S12 derivatives which have bus speeds of up to 25 MHz and flash sizes up to 512 kB.The MC9S12NE64 was introduced by Freescale in September 2004, claiming to be the "industry's first single-chip fast-Ethernet Flash microcontroller." It features a 25 MHz HCS12 CPU, 64 kB of FLASH EEPROM, 8 kB of RAM, and an Ethernet 10/100 Mbit
Megabit
The megabit is a multiple of the unit bit for digital information or computer storage. The prefix mega is defined in the International System of Units as a multiplier of 106 , and therefore...
/s controller.
MC9S12X derivatives
The MC9S12XDP512 which was introduced in 2004 has a bus speed of 40 MHz and a peripheral co-processor known as the XGATE which allows for some tasks to be offloaded from the CPU. The CPU of the S12X derivative also features several new instructions to increase performance.Freescale announced the MC9S12XEP100 in May 2006 to further extend the S12X family to 50MHz bus speed and add a Memory protection
Memory protection
Memory protection is a way to control memory access rights on a computer, and is a part of most modern operating systems. The main purpose of memory protection is to prevent a process from accessing memory that has not been allocated to it. This prevents a bug within a process from affecting...
unit (based on segmentation
Segmentation (memory)
Memory segmentation is the division of computer memory into segments or sections. Segments or sections are also used in object files of compiled programs when they are linked together into a program image, or when the image is loaded into memory...
) and a hardware scheme to provide Emulated EEPROM
EEPROM
EEPROM stands for Electrically Erasable Programmable Read-Only Memory and is a type of non-volatile memory used in computers and other electronic devices to store small amounts of data that must be saved when power is removed, e.g., calibration...
.
HCS12 products contain a single processor, the HCS12X feature the additional XGATE peripheral processor.
The XGATE co-processor is a 16-bit RISC processor operating at twice the main bus clock. It offloads work from the HC12 core by handling interrupts only and does not run a background loop. The first versions of the XGATE do not allow for higher priority interrupts to pre-empt a currently handled interrupt, but the "XGATEV3" as featured in the 9S12XEP100 does allow this. The HC12 can trigger software interrupts on the XGATE core. A semaphore system is implemented to allow the S12X and XGATE cores to share peripherals.
External links
- Free real-time kernel source code for HCS12 with sample apps
- Freescale's official OpenTCP project on SourceForge for MC9S12NE family
- http://hc12text.com/
- http://ee.cleversoul.com/hc12.html
- http://hc12web.de/
- DRAGON12-Plus HCS12/9S12 Trainer, EVB and Development Board
- MiniIDE development environment that works with both 68HC11 and 68HC12
- Open source editor with syntax highlighting for the HCS12(X)
- 68HC12 Discussion Group
- 68HC12 Development and training system