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Difficulty: HardNetwork and Peripheral Cables and Connectors

A technician is connecting a modern maintenance laptop that features only USB Type-C ports to an legacy industrial control unit that requires a direct RS-232 serial interface via a male DB-9 connector. The connection must allow terminal communication without using network connectivity. Which cable or adapter configuration provides the necessary physical connection and protocol translation for this setup?

  1. A USB Type-C to male DB-9 cable containing an integrated active RS-232 serial bridge chipsetAnswer
  2. B
    A passive USB Type-C to DB-9 adapter relying on USB-C DisplayPort Alternate Mode to pass serial signals
  3. C
    A standard T568B RJ-45 Ethernet patch cable fitted with passive RJ-45 to DB-9 modular adapters on both ends
  4. D
    A USB Type-C to VGA adapter connected to a passive VGA-to-DB-9 adapter cable

Answer

A USB Type-C to male DB-9 cable containing an integrated active RS-232 serial bridge chipset
RS-232 serial communications require specific voltage levels and asynchronous data framing that are fundamentally different from USB signals. Connecting a modern laptop via USB Type-C to an RS-232 DB-9 serial port requires an active adapter containing a USB-to-Serial bridge chip (e.g., FTDI chipset) to convert the protocols dynamically.

Step-by-Step Solution

1
Identify the host and target port types and protocols
Host uses USB Type-C (digital USB protocol); target uses DB-9 RS-232 (legacy serial protocol).
Determines whether passive pin mapping or active protocol conversion is required.
2
Evaluate signal compatibility between USB and RS-232
USB and RS-232 use completely different signal levels, timing, and framing mechanisms, requiring an active converter circuit (such as FTDI or Prolific chipsets).
Passive adapters cannot translate USB packets into RS-232 bitstreams.
3
Select the correct adapter solution
A USB Type-C to DB-9 cable with an integrated active RS-232 serial bridge chipset bridges both the physical interface and protocol gap.
It supplies native serial communication capabilities to modern laptops lacking built-in COM ports.

Key Concept

RS-232 Serial to USB Protocol Conversion and DB-9 Connectors
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Topics

Network and Peripheral Cables and Connectors

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