📖 14. Serial Communication and Programmable Communication Interface

📖 From An Introduction To Microprocessor 8085 • 174 questions available

About 14. Serial Communication and Programmable Communication Interface

Parallel communication, where you send 8 bits at a time over 8 wires, is fast but expensive over long distances (imagine a printer cable that's 100 meters long). Serial communication sends data one bit at a time, one after the other, over a single wire. This is cheaper and more practical for long distances (like a modem or serial mouse). This chapter covers the principles of serial data transfer and introduces a support chip (like the 8251 USART—Universal Synchronous/Asynchronous Receiver/Transmitter) that handles the complex job of converting parallel data from the 8085 into serial data and vice versa.

How It Works: You learn about two main types of serial communication: Asynchronous (where there is no separate clock signal, and data is sent in small packets with start and stop bits—like old COM ports) and Synchronous (where a separate clock signal is used, allowing for faster and more efficient data transfer). The 8251 is a programmable chip that the CPU configures to set the baud rate (speed), data format (number of data bits, parity, stop bits), and mode. The CPU sends a byte to the 8251 to transmit, and the 8251 automatically shifts it out bit-by-bit. For receiving, the 8251 gathers the incoming bits, assembles them into a byte, and signals the CPU that it's ready.

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🔄 Last updated: 2026-07-30