Microprocessor Architecture and Industrial Control Systems

Types of Control Systems

• Programmable Controllers: These firmware systems are based on a microcontroller chip integrated into power control systems, such as contactors or relays. They are intended to control industrial machinery and automation.
• Small Automatic Systems: These systems are governed by microprocessors, microcontrollers, and PIC microcontrollers. They are used for controlling appliances, illuminated signs, programmable calculators, and small alarm systems.

Internal CPU Architecture

The internal CPU consists of the following essential elements:

• Processing unit (Arithmetic Logic Unit - ALU)
• Control unit (Decoding and interpretation)
• Accumulator and registers
• Program counter

The Processing Unit

The Processing Unit is the area where arithmetic and logical operations are performed using data from the main memory or internal registers. It also manages all data transfers to and from the memory. It comprises the Arithmetic Logic Unit (ALU), the accumulator, and the status register.

ALU, Accumulators, and Registers

The ALU (Accumulators and registers) serves as a small internal memory for the microprocessor, where intermediate results of operations are temporarily stored.

Registers consist of bistables positioned to store information at a given time. The register length is determined by the number of bistables. All operations are conducted through the accumulator, with the final results appearing within it.

The Control Unit

The Control Unit is the most important part of the microprocessor and is responsible for governing its overall operation. It contains the following elements:

• Program counter
• Instruction register
• Instruction decoder
• Clock
• Sequencer

The control unit also contains another set of records for internal registers (instructions, directions, and data), auxiliary registers, and the SP (Stack Pointer) register.

System Clock and Synchronization

The Clock generates all necessary signals to control the other blocks of the system. To ensure the entire system remains in sync, it utilizes a constant frequency square wave generated by a quartz crystal.

The frequency of this clock is measured in MHz and determines the operating speed and processing power of the microprocessor. The period of this clock is referred to as the clock cycle.