Lecture 7: Interfacing and Communications

Difference between Interfacing and Communicating:

• Interfacing is about connecting devices safely and reliably, including physical connectors, voltage levels, and input/output signals.

• Communicating refers to sending messages or data between devices, including timing signals and protocols.

Describe the basic principles of interfacing an LCD display and a keyboard in an embedded system

• LCD display interfacing requires enabling the device, selecting registers, and setting up data pins.

• Keyboard interfacing uses a scanning method where multiple pins are initialized to detect key presses, often requiring pull-down resistors to stabilize inputs.

• What is the difference between parallel and serial comms?

• Parallel: Uses multiple wires to transmit multiple bits simultaneously. It provides high throughput over short distances but can be bulky and expensive.

• Serial: Transmits data one bit at a time over a single wire, making it more efficient for long distances but requiring more complex processing.

What are the differences between asynchronous and synchronous communications?

• Asynchronous: Each device has its own oscillator and timing is not shared (e.g., RS-232, USB).

• Synchronous: A separate clock signal is provided by the master device to synchronize data transmission (e.g., SPI, I2C).

Discuss the operating principles of the SPI and RS-232 communications

• SPI (Serial Peripheral Interface): Full-duplex communication using separate clock and slave select lines. It is fast but requires multiple connections.

• RS-232: A UART-based asynchronous serial communication method that converts parallel data into serial format and includes parity bits for error checking.

Name two communication modes for the PIC16F887. Is it possible to have full duplex communication in the synchronous mode?

• The PIC16F887 supports Asynchronous Full-Duplex Mode and Synchronous Half-Duplex Mode.

• Full duplex is not possible in synchronous mode because synchronous communication only allows either transmission or reception at a time.

• Discuss the use of the PIC USART for synchronous TX

In synchronous mode, the PIC USART acts as a master or slave. The master provides a clock, and transmission happens half-duplex with synchronization.

• Discuss the use of the PIC USART for asynchronous TX

Asynchronous mode supports full-duplex communication using separate TX and RX lines. Baud rate errors must be managed carefully.

• What does using protocols add to communications?

Protocols define structured communication processes using packets instead of raw byte transfer. They improve efficiency, enable error detection, and support multi-device communication.

• Name three synchronous communication protocols

SPI, I2C, CAN (Controller Area Network).