Classification of Microcontrollers

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.

Types of Microcontroller:

The microcontrollers are characterized regarding bus-width, instruction set, and memory structure. This article is going to describe some of the basic types of the Microcontroller that newer users may not know about. So the microcontroller can be classified according to their charecteristics as shown in graph below:

Bits:

• The bits in microcontroller are 8-bits, 16-bits and 32-bits microcontroller.In 8-bit microcontroller, the point when the internal bus is 8-bit then the ALU is performs the arithmetic and logic operations. The examples of 8-bit microcontrollers are Intel 8031/8051, PIC1x and Motorola MC68HC11 families.
• The 16-bit microcontroller performs greater precision and performance as compared to 8-bit. For example 8 bit microcontrollers can only use 8 bits, resulting in a final range of 0×00 – 0xFF (0-255) for every cycle. In contrast, 16 bit microcontrollers with its 16 bit data width has a range of 0×0000 – 0xFFFF (0-65535) for every cycle. A longer timer most extreme worth can likely prove to be useful in certain applications and circuits. It can automatically operate on two 16 bit numbers. Some examples of 16-bit microcontroller are 16-bit MCUs are extended 8051XA, PIC2x, Intel 8096 and Motorola MC68HC12 families.
• The 32-bit microcontroller uses the 32-bit instructions to perform the arithmetic and logic operations. These are used in automatically controlled devices including implantable medical devices, engine control systems, office machines, appliances and other types of embedded systems. Some examples are Intel/Atmel 251 family, PIC3x.

Memory/Devices:

Embedded microcontroller: When an embedded system has an MCU that has all the hardware and software units in a single unit, the MCU is called embedded microcontroller. Very few or no other external unit or system is present for processing during the control or use of the external devices. For example, a telephone handset circuit uses an embedded microcontroller.

External memory microcontroller: When an embedded system has an MCU that has all the hardware and software units present not as a single unit and has all or part of the memory unit externally interfaced using an interfacing circuit which is called the glue circuit, the MCU is called an external memory microcontroller. For example, 8031 has the program memory which is interfaced externally to it. The 8051 has both internal as well as external program memory.

Family:

The microcontrollers can also be classified according to their family. family is usually a company or a manufacturer in which controller is fabricated. Each family have its own architecture and instruction set. some though 8051 is famous but PIC and ARM are going more popular than 8051.

Instruction Set:

Complicated Instruction Set Computer (CISC) architecture microcontroller: When an MCU has an instruction set that supports many addressing modes for the arithmetic and logical instructions and when there are the memory accesses during the ALU operations and the data transfer instructions, the MCU is said to be possessing CISC-architecture.

CISC provides flexibility in choosing various ways of performing the data transfer, arithmetic and other operations. For example, it is feasible to add contents of two registers or add the register and memory or add the bits at two memory addresses in a CISC. Instructions are of variable number of bytes in the CISC. These can take varying amounts of time interval for execution. An example is Intel 8096.

Reduced Instruction Set Computer (RISC) microcontroller: When an MCU has an instruction set that supports a few addressing modes for the arithmetic and logical instructions and just a few (load, store, push and pop) instructions for the data transfer, the MCU is said to be of RISC architecture. RISC provides no flexibility in choosing the many different ways of performing the arithmetic and logic operations. These operations are performed after the load of operands in the registers, and the results of these operations are placed in registers. The register contents are later on stored in the memory. RISC implements each instruction in a single cycle using a distinct hardwired control. It uses a lesser amount of circuitry. It has less power dissipation. There is reduced instruction set. Instructions are of fixed number of bytes and take a fixed amount of time for execution. It has many registers. Therefore, operations can be performed using them. The need for external fetches from the memories are greatly reduced. (An external fetch is to be done by the CPU for an operand more frequently in the CISC). The RISC provides a higher performance in computing than the CISC. This is because little need of the external fetches, which takes a significant amount of processor time. High performance is also because of hardwired implementation of instructions. An example of RISC architecture is the ARM processor family-based MCU

Memory Architecture:

• Harvard Memory Architecture Microcontroller: The point when a microcontroller unit has a dissimilar memory address space for the program and data memory, the microcontroller has Harvard memory architecture in the processor.
• Princeton Memory Architecture Microcontroller: The point when a microcontroller has a common memory address for the program memory and data memory, the microcontroller has Princeton memory architecture in the processor.

This is how the MICs are classified, there may be some other types but most of the types can be seen through this major classification.