StarTech.com DB9 RS232 Serial Null Modem Adapter

Introduction

The StarTech.com NM9FF Null Modem Adapter is designed to facilitate direct data transfer between two Data Terminal Equipment (DTE) devices, such as computers or terminals, using standard serial cables. This adapter converts a straight-through serial cable into a null modem configuration by internally crossing the transmit (TX) and receive (RX) data lines, as well as the corresponding handshaking lines. It features two DB9 female connectors, providing a convenient and cost-effective solution for serial communication without the need for specialized null modem cables.

Safety Information

Always read and follow all safety instructions to reduce the risk of injury, electric shock, fire, or damage to equipment.

• Electrical Hazards: Ensure all cables are properly insulated and connected to avoid short circuits or fires.
• Trip Hazards: Secure cables along walkways to prevent trips and falls.
• Cable Damage: Avoid pinching, kinking, or pulling cables excessively. Damaged cables can expose wires, causing a risk of shock or device failure.
• Heat Buildup: Do not bundle cables too tightly, as this can cause overheating. Ensure proper ventilation.

Image: A multilingual safety warning sheet detailing electrical hazards, trip hazards, cable damage, and heat buildup warnings.

Package Contents

• 1 x StarTech.com DB9 RS232 Serial Null Modem Adapter (NM9FF)
• 2 x Thumbscrews (pre-attached)
• 4 x Hex stand-offs (included for optional use)

Image: The StarTech.com DB9 RS232 Serial Null Modem Adapter (NM9FF) shown with its two DB9 female ports and four small hex stand-offs.

Image: The NM9FF adapter sealed in its clear plastic retail packaging, displaying the StarTech.com branding and product details.

Setup

1. Identify Devices: Determine the two DTE devices (e.g., computers, routers, switches) you wish to connect using a serial cable.
2. Prepare Cables: Ensure you have one or two standard straight-through DB9 serial cables.
3. Connect Adapter: Plug one end of a straight-through DB9 serial cable into one of the female DB9 ports on the NM9FF adapter. Secure the connection using the integrated thumbscrews on the adapter.
4. Connect to Device 1: Plug the other end of the serial cable into the DB9 serial port of your first DTE device.
5. Connect to Device 2: Plug the second female DB9 port of the NM9FF adapter directly into the DB9 serial port of your second DTE device. Alternatively, if using two straight-through cables, connect the second cable to the adapter and then to the second device. Secure all connections.

Image: A side profile view of the NM9FF adapter, showing its compact design and the thumbscrews on both ends.

Image: A detailed close-up of one of the DB9 female connectors on the adapter, clearly showing the nine pinholes and the numbering.

Operating Principles

A null modem adapter is essential when connecting two DTE devices directly without a modem or other Data Communications Equipment (DCE). It achieves this by internally re-routing the serial communication lines. Specifically, it crosses the transmit data (TXD) line of one device to the receive data (RXD) line of the other, and vice-versa. It also typically crosses the Request To Send (RTS) and Clear To Send (CTS) handshaking lines.

The NM9FF adapter implements the following common null modem pinout:

• Pin 1 (DCD) <-> Pin 1 (DCD)
• Pin 2 (RXD) <-> Pin 3 (TXD)
• Pin 3 (TXD) <-> Pin 2 (RXD)
• Pin 4 (DTR) <-> Pin 6 (DSR)
• Pin 5 (GND) <-> Pin 5 (GND)
• Pin 6 (DSR) <-> Pin 4 (DTR)
• Pin 7 (RTS) <-> Pin 8 (CTS)
• Pin 8 (CTS) <-> Pin 7 (RTS)
• Pin 9 (RI) <-> Pin 9 (RI)

This configuration allows the two DTE devices to communicate as if they were connected via a modem, enabling applications like file transfer, console access to network equipment, or direct PC-to-PC communication.

Maintenance

The StarTech.com NM9FF Null Modem Adapter requires minimal maintenance. To ensure optimal performance and longevity:

• Cleaning: Use a soft, dry cloth to wipe the exterior of the adapter. Avoid using liquid cleaners or solvents, as they may damage the plastic or internal components.
• Storage: Store the adapter in a cool, dry place away from direct sunlight and extreme temperatures when not in use.
• Handling: Handle the adapter by its body, avoiding excessive force on the connectors or cables.

Troubleshooting

If you experience issues with your null modem connection, consider the following:

• No Communication:
  • Ensure all cables are securely connected to the adapter and devices.
  • Verify that the serial ports on both devices are enabled and configured correctly (e.g., baud rate, data bits, parity, stop bits). These settings must match on both ends.
  • Confirm that the software or application attempting to use the serial port is correctly configured and not conflicting with other processes.
• Incorrect Data:
  • Double-check the serial port settings (baud rate, data bits, parity, stop bits) on both connected devices. A mismatch will result in garbled data.
  • Ensure you are using a standard straight-through serial cable with the null modem adapter, not another null modem cable, which would result in a double-cross.
• Physical Damage: Inspect the adapter and cables for any visible signs of damage, such as bent pins or frayed wires. Replace damaged components if necessary.

Specifications

Warranty and Support

This StarTech.com product is backed by a Lifetime Warranty. For technical support, product information, or warranty claims, please visit the official StarTech.com support website or refer to the contact information provided with your product packaging.

You can find more information and support resources at: startech.com/q/NM9FF