6.1 State TWO uses of a microcontroller as used in commercial devices - NSC Electrical Technology Digital - Question 6 - 2024 - Paper 1

The block diagram in FIGURE 6.2 above represents a microcontroller, which integrates the central processing unit (CPU), read-only memory (ROM), random access memory (RAM), and input/output (I/O) components.

The control bus is used primarily for the CPU to issue control instructions to both memory and input/output ports.

The data bus serves as the 'highway' through which all data is transferred, sent, and received between the CPU, memory, and both input and output ports.

An interface is a shared boundary across which two separate components of a computer system exchange information.

Upon entering the current instruction register (CIR) from the Memory Data Register (MDR), the data is split into two parts: one part is decoded by the control unit for execution, and the other part includes the address of the data that the instruction will use.

The accumulator functions as a storage area for data that is needed for arithmetic and logic operations within the CPU.

• General purpose registers: These registers can store temporary data and are utilized for various operations during program execution.
• Special purpose registers: These are specifically designed for particular tasks, such as maintaining the current instruction or address in the memory.

Communication protocols are sets of rules that allow two electronic devices to connect and exchange data effectively.

Simplex communication allows data to travel in one direction only, meaning the transmitter can send data, but cannot receive data back. In contrast, half-duplex communication enables devices to send and receive data, but not simultaneously; they must take turns communicating.

The serial peripheral interface (SPI) is a communication protocol that operates in full duplex mode, utilizing separate clock and data lines. This allows data to be transmitted in both directions simultaneously.

• Susceptibility to noise: Since SPI uses direct connections, it is more likely to pick up noise, especially over longer distances.
• Distance limitations: SPI can only operate over short cable lengths compared to other communication protocols.

The maximum cable length for RS-485 communication is 1200 metres.

The mode of operation for RS-485 is simplex or half-duplex, enabling data exchange in both single-direction or alternate turn-taking.

• Point of Sale (POS) terminals: Used for processing sales transactions.
• CNC machines: Employed in manufacturing for computer-controlled operations.

In the instruction cycle, the CPU fetches a program instruction from its memory, decodes it to understand what action to perform, considers all input signals, and then executes the instruction accordingly.

The flow chart should depict the following steps:

1. Start
2. Check if the switch is pressed:
   • If Yes, go to Output ON.
   • If No, loop back to check again.
3. Output ON
4. Wait for 5 seconds
5. Output OFF
6. Loop back to check if the switch is pressed.