Parallel–serial interfacing — Which device is typically used to bridge a microprocessor’s parallel data bus to an external serial communications format?

Introduction:
Systems often need to communicate over serial links (e.g., RS-232, RS-485, UART-over-USB) while the CPU presents data on a parallel bus. A dedicated interface device performs the format conversion and handles timing details.

Given Data / Assumptions:

• Microprocessor or MCU provides data bytes in parallel.
• External channel expects asynchronous serial frames.
• Standard start/stop bit framing and optional parity are required.

Concept / Approach:

A UART (Universal Asynchronous Receiver/Transmitter) converts between parallel and serial data. On transmit, it frames bytes with start/stop (and parity) and shifts them out at the selected baud rate. On receive, it samples the serial line, reconstructs the byte, checks parity/stop, and presents parallel data to the system.

Step-by-Step Solution:

Verification / Alternative check:

MCU block diagrams and PC serial ports universally feature UARTs for parallel–serial translation, confirming their role as the standard interface component.

Why Other Options Are Wrong:

• Key matrix: Scans switches; not a serial converter.
• Memory chip: Stores data; no serial framing.
• Serial-in, parallel-out: Does the opposite direction and lacks framing logic.
• ADC with SPI: SPI is synchronous serial; still not the generalized asynchronous serial interface described.

Common Pitfalls:

• Mismatching baud rate, parity, or stop bits between endpoints.
• Ignoring buffering/interrupts, causing overruns at higher speeds.

Final Answer:

UART