[1] Normal density of DA, DB, DC, DD, and DE sized connectors
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D-subminiature
D-subminiature
[1] The D-subminiature/D-sub is a common electrical connector type, named for their characteristic D-shaped metal shield, often for RS232 serial communications. In their introduction, they were among the smallest connectors in personal computer systems.
The DB9/D9 connector is a type of 9-pin electronic D-sub connector, the most common of its 9-pin connector, which has 9 pins.
Despite widely being called "DB9", the actual name is DE9, where "B" was earlier used to refer to standard 25-pin serial connectors that used a "B" sized shell, called DB-25. Later as computers used 9-pin connectors, industries used the "B" by accident, when 9-pin connectors actually use "E" sized shells.
It's eventually replaced by smaller faster data-transferring plugs like USBs.
Properties and features
Properties and features
DE9 cables
Durability: DE9 cables' metal shield protects pins and provides great shielding against electrical noise (EMI). [6] It's made of robust materials like metal or plastic for long-term and reliability in harsh environments.
EMI shielding: A metal shield often surrounds the connector, protecting against electromagnetic interference (EMI), which is crucial in industrial and telecommunications applications.
Versatility: DB9 connectors can be used in a wide range of devices, from computers and modems to industrial equipment and embedded systems.
Legacy support: Though newer systems use USB or wireless connections, DB9 is relevant to support older devices and legacy systems.
Types
Types
The distinction of male and female DB9 connectors is based on their contact points, which ensures cables and devices only connect the intended way.
A "male" connector has a solid pins per center conductor.
A "female" connector has a hole per conductor for the male pin.
Standard PC serial port uses a "female" RS232 connector.
Note: To recall a cable's "gender", know that "male" DB9 connectors' pins (the plug) penetrate the "female" (the socket) which have holes instead, to reflect to private parts in real life.
[M1]
[M3]
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Pinouts
Pinouts
DE9 cables have a standardized pinout to ensure compatibility across different devices (same numberings and functionality for each pins).
[M1]
Transmit data (TD): sreial data output (TXD)
Receive data (RD): serial data input (RXD)
Clear to send (CTS) indicates that th emodem is ready to exchange data.
Data carier detect (DCD): If the modem detects a carrier form the modem at the other end of the phone line, this line becomes active
Ground (GND) provides common a safe electrical baseline.
Data set ready (DSR) tells the UART tat the modem is ready to establish a likn.
Data terminal ready (DTR) is the opposite to DSR, telling the modem that the UART is ready to link.
Request to send (RTS) informs the modem that is ready to exchange data.
Ring indicator R1) goes active if modem detects a ringing signal from the PSTN.
It's crucial to know that for a male DB9 connector, its pin numbers start from left to right and for a female DB9 connector, from right to left, as shown below - thus mirroring each other since they connect together.
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[5]
[M1]
[M1]
Description, nomenclature, and variants
Description, nomenclature, and variants
[1] A D-sub has 2+ parallel rows of pins or sockets often surrounded by a D-shaped metal shield for mechanical support, ensures correct orientation, and may screen against electromagnetic interference.
Calling that shield a shell (or D-shell) can be ambiguous, as the term shell is also short for the cable shell, or backshell. D-sub connectors have gender: parts with pin contacts are called male connectors or plugs, while those with socket contacts are called female connectors or sockets. The socket's shield fits tightly inside the plug's shield. Panel-mounted connectors usually have #4-40 UNC (as designated with the Unified Thread Standard) jackscrews that accept screws on the cable end connector cover that are used for locking the connectors together and offering mechanical strain relief, and can be tightened with a 3/16" (or 5mm) hex socket.
Troubleshooting
Troubleshooting
[2.1] Testing if adapter is sending/receiving data via the loopback test Bridging the transmit and receive pins (TD and RD pins) creates a "hardware echo", the result of bridging. If what we type comes back, the adapter works correctly.
We start bridging pins 2 and 3 (TD and RD) via a small screwdriver to touch both pins. Or we can use a a U-shaped bent paperclip to connect to one of the DB9 connector's TD and RD pins on a female-to-female RS232 DB9 cable. Using a paperclip is the better method as it ensures a more secure connection.
bridge: to physically and electrically connect between 2 pins on serial connector yto force cable output to feed d directly bakc to own input
hardware echo: result of "bridging"
[2.1] Then plug the other female DB9 connector to a male connector and plug the USB end of the male connector to your laptop.
a[2.1] In laptop: Device manager → Ports (COM & UPT) (COM port number) → Connected connector's name → Open "PuTTY (a free terminal emulator and network file transfer application) → Set connection type as Serial → Change serial line name to match the adapter name in Device manager → Open (open the terminal, which should be a black space to enter texts) →
[2.1With the connector's pins bridged, any text we send should be received back to us ("looping" back). So we must type texts in the terminal window. If every character type on the keyboard appears on onscreen accordingly, things work correclty.
If no characters or if the wrong ones appear, then looping is failing.
My materials
My materials
[M2] ELE8940 Week 6: RS232 (Canva)
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