DB9 Serial Interfaces
Last Updated: April 1, 2025
Description
The DB9 serial interface is a type of connector used for serial communication, typically featuring a 9-pin configuration. It is commonly associated with the RS-232 standard, which is used for data exchange between computers and peripheral devices. The DB9 connector facilitates the transmission and reception of data through its pins, which are designated for specific functions such as transmitting data, receiving data, and providing a common ground.
Working Principle
The DB9 serial interface operates on the principle of serial communication, where data is transmitted one bit at a time over a single communication line. This method is efficient for long-distance communication as it requires fewer wires compared to parallel communication. The DB9 connector typically uses the RS-232 standard, which involves a set of electrical characteristics and protocols for data transmission. The interface supports simplex, duplex, and full duplex communication modes, allowing for one-way or two-way data exchange. The RS-232 standard specifies voltage levels for binary data, with positive voltages representing a binary '0' and negative voltages representing a binary '1'. This setup is useful for connecting various devices, ensuring compatibility and reliable data transfer.
Applications
DB9 serial interfaces are widely used in various applications due to their simplicity and reliability. In computing, they are often employed to connect peripheral devices such as mice, keyboards, and modems to computers. In industrial automation, DB9 connectors are used to link programmable logic controllers (PLCs) and other control systems, facilitating communication between sensors and central control units. Additionally, they are utilized in telecommunications for connecting network equipment and in medical devices for data exchange between diagnostic equipment and computers.
Advantages over other Serial Interfaces
One of the primary advantages of the DB9 serial interface, particularly when using the RS-232 standard, is its simplicity and cost-effectiveness. It requires fewer wires, which reduces the complexity and cost of cabling. The DB9 connector is also widely recognized and supported, making it a versatile choice for connecting a broad range of devices. Compared to more modern interfaces, the DB9's straightforward design and established standardization make it a reliable option for legacy systems and applications where high-speed data transfer is not critical.
Limitations
The DB9 serial interface, while reliable, has several limitations. The RS-232 standard, commonly associated with DB9 connectors, supports a maximum baud rate of 20,000 bps, which is relatively slow compared to modern communication standards. This limits its use in applications requiring high-speed data transfer. Additionally, the DB9 interface is not suitable for multi-point communication, as it is designed for point-to-point connections. The physical size of the connector can also be a drawback in applications where space is limited.
Considerations
When considering the use of DB9 serial interfaces, several factors should be taken into account. Initial costs are generally low due to the simplicity of the connector and cabling. Operating expenses are minimal, as the interface is durable and requires little maintenance. However, the limited data transfer speed may necessitate additional investment in more advanced interfaces for applications requiring higher performance. The DB9 connector is robust and reliable, but its larger size may not be suitable for compact or portable devices. Replacement and maintenance costs are typically low, but availability of compatible devices and components should be considered, especially for newer systems.
from Advantech
Isolated RS-232, 2-Ports, DB9, PCIe I/F. Meets Advantech Standard iDoor Technology. PCI Express ® Mini Card Specification Revision 1.2 compliant. Speeds up to 921.6 kbps for extremely fast data transmission. Supports any baud rate setting (50bps~921.6kbps). Supports both Isolated &... [See More]
- Connector: DB9; 2 x Male DB9
- Network / Bus: PCI; PCI Express Mini Card Revision 1.2
- Serial Protocol: RS232
- Data Rate: 0.0500 to 922
from Connect Tech Inc.
Frees devices from a physical PC connection [See More]
- Connector: DB9; RJ-45
- Network / Bus: BACnet; DNP3; 10Base-T; Modbus; 100Base-TX
- Serial Protocol: RS232
- Data Rate: 461
from American Portwell Technology Inc.
Self powered DB9 RS-232 to DB9 RS-422 Serial Data Converter [See More]
- Connector: DB9
- Network / Bus: USB
- Serial Protocol: RS232; RS422
- Form Factor: Portable
from ACCES I/O Products, Inc.
Features. Universal PCI, PCI-X, 3.3V and 5V compatible (Call for PCI-Express availability). Dual-port serial communications card for PCI bus. Supports RS-232(PCI-COM2S only), RS-422, and RS-485 protocols. Automatic control of RS-485 driver under Windows systems. Includes type 16550 UART with 16-byte... [See More]
- Connector: DB9
- Network / Bus: PCI
- Serial Protocol: RS422; RS485
- Operating System: Windows XP Through Windows 8.1, Including "Server 2008," "Embedded," and "Compact" Flavors in Both 32-bit and 64-bit for All Plug-and-play Products
from Moxa Inc.
The TCF-90 is a compact media converter that transmits RS-232 signals over optical fiber. Power is derived from either the serial port or an external power source. The TCF-90 extends RS-232 transmission up to 5 km with multi-mode fiber, or up to 40 km with single-mode fiber. A pair of TCF-90... [See More]
- Connector: DB9
- Data Rate: 115
- Serial Protocol: RS232
- Number of Ports: 1
from Opto 22
The SNAP-SCM-PROFI module is a high-speed serial communications module that provides a standard electrical interface between the Ethernet-based SNAP PAC System and PROFIBUS DP ® networks. The SNAP-SCM-PROFI module is designed for use with Opto 22 ’s SNAP PAC brains and R-series... [See More]
- Connector: DB9
- Data Rate: 1500
- Network / Bus: PROFIBUS; SNAP Brains
- Number of Ports: 1
from Sealevel Systems, Inc.
This product is classified as legacy and is not recommended for new or high volume designs. Sealevel will support legacy products through technical and warranty support, software drivers and product manuals. Please contact Sales for further information. For new product designs, we recommend the... [See More]
- Connector: DB9
- Network / Bus: CompactPCI
- Serial Protocol: RS232/422/485
- Data Rate: 922
from American Portwell Technology Inc.
Self powered DB9 RS-232 to DB9 RS-485 Serial Data Converter [See More]
- Connector: DB9
- Network / Bus: USB
- Serial Protocol: RS232; RS485
- Form Factor: Portable
from ACCES I/O Products, Inc.
Features. Universal PCI, PCI-X, 3.3V and 5V compatible (Call for PCI-Express availability). Optically isolated, asynchronous serial communications. Two independent ports each supports RS-422 or RS-485 communications. Type 16550 buffered UARTs protect against data loss in multitasking systems. Baud... [See More]
- Connector: DB9; 68-pin, Shielded, VHDCI Connector
- Network / Bus: PCI
- Serial Protocol: RS422; RS485
- Operating System: Windows XP Through Windows 8.1, Including "Server 2008," "Embedded," and "Compact" Flavors in Both 32-bit and 64-bit for All Plug-and-play Products
from Sealevel Systems, Inc.
This product is classified as legacy and is not recommended for new or high volume designs. Sealevel will support legacy products through technical and warranty support, software drivers and product manuals. Please contact Sales for further information. For new product designs, we recommend the... [See More]
- Connector: DB9
- Network / Bus: CompactPCI
- Serial Protocol: RS232/422/485
- Data Rate: 461
from American Portwell Technology Inc.
USB to single DB9 RS-232 with included cable [See More]
- Connector: DB9
- Network / Bus: USB
- Serial Protocol: RS232
- Number of Ports: 1
from ACCES I/O Products, Inc.
Features. Universal PCI, PCI-X, 3.3V and 5V compatible (Call for PCI-Express availability). Four-port serial communications card for PCI bus. Supports RS-422 protocol. Includes type 16550 UART with 16-byte FIFO buffers. Baud rates up to 460,800 baud. Choice of I/O connection methods. Detected as... [See More]
- Connector: DB9
- Network / Bus: PCI
- Serial Protocol: RS422
- Operating System: Windows XP Through Windows 8.1, Including "Server 2008," "Embedded," and "Compact" Flavors in Both 32-bit and 64-bit for All Plug-and-play Products
from Sealevel Systems, Inc.
This product is classified as legacy and is not recommended for new or high volume designs. Sealevel will support legacy products through technical and warranty support, software drivers and product manuals. Please contact Sales for further information. For new product designs, we recommend the... [See More]
- Connector: DB9
- Network / Bus: CompactPCI
- Serial Protocol: RS232/422/485
- Data Rate: 461
from American Portwell Technology Inc.
USB to single DB9 RS-422 with included cable [See More]
- Connector: DB9
- Network / Bus: USB
- Serial Protocol: RS422
- Number of Ports: 1
from ACCES I/O Products, Inc.
Features. Universal PCI, PCI-X, 3.3V and 5V compatible (Call for PCI-Express availability). Four-port serial communications card for PCI bus. Supports RS-485 multidrop networks. Includes type 16550 UART with 16-byte FIFO buffers. Baud rates up to 460,800 baud. Automatic control of RS-485 driver... [See More]
- Connector: DB9
- Network / Bus: PCI
- Serial Protocol: RS485
- Operating System: Windows XP Through Windows 8.1, Including "Server 2008," "Embedded," and "Compact" Flavors in Both 32-bit and 64-bit for All Plug-and-play Products
from Sealevel Systems, Inc.
The 3088 ISA serial interface provides PC systems with two RS-232 Asynchronous links to data collection and other devices. Modems, data entry terminals and plotters are some devices that use RS-232 protocols. The 3088 allows for individually selectable interrupts (2-5, 7, 10-12 and 15). This product... [See More]
- Connector: DB9
- Data Rate: 115
- Serial Protocol: RS232
- Number of Ports: 2
from American Portwell Technology Inc.
USB to single DB9 RS-485 with included cable [See More]
- Connector: DB9
- Network / Bus: USB
- Serial Protocol: RS485
- Number of Ports: 1
from Sealevel Systems, Inc.
The 3087 ISA serial interface provides two RS-232, RS-422, or RS-485 Asynchronous links to data collection and other devices. Fully independent operation of ports allows the configuration of the 3087 with either two RS-232 ports, two RS-422, RS-485 ports or with a combination of one RS-232 port and... [See More]
- Connector: DB9
- Data Rate: 115
- Serial Protocol: RS232/422/485
- Number of Ports: 2
from Sealevel Systems, Inc.
THIS PRODUCT IS OBSOLETE DUE TO LACK OF COMPONENT AVAILABILITY. PLEASE CONTACT YOUR SALES REPRESENTATIVE FOR FURTHER INFORMATION AND NEW PRODUCT ALTERNATIVES. Sealevel will support legacy products through technical and warranty support, software drivers and product manuals. Please contact Sales for... [See More]
- Connector: DB9
- Data Rate: 115
- Serial Protocol: RS232/422/485
- Number of Ports: 2
from Sealevel Systems, Inc.
THIS PRODUCT IS OBSOLETE DUE TO LACK OF COMPONENT AVAILABILITY. PLEASE CONTACT YOUR SALES REPRESENTATIVE FOR FURTHER INFORMATION AND NEW PRODUCT ALTERNATIVES. Sealevel will support legacy products through technical and warranty support, software drivers and product manuals. Please contact Sales for... [See More]
- Connector: DB9
- Data Rate: 115
- Serial Protocol: RS232/422/485
- Number of Ports: 2
from Sealevel Systems, Inc.
THIS PRODUCT IS OBSOLETE DUE TO LACK OF COMPONENT AVAILABILITY. PLEASE CONTACT YOUR SALES REPRESENTATIVE FOR FURTHER INFORMATION AND NEW PRODUCT ALTERNATIVES. Sealevel will support legacy products through technical and warranty support, software drivers and product manuals. Please contact Sales for... [See More]
- Connector: DB9
- Data Rate: 461
- Serial Protocol: RS232/422/485
- Number of Ports: 4
from Sealevel Systems, Inc.
The 7104 Low Profile PCI serial interface provides one RS-232 serial port capable of data rates to 460.8K bps. The board utilizes a 16C850 UART to provide 128-byte Tx/Rx FIFOs for maximum reliability in data intensive applications. The Sealevel SeaCOM software driver and utilities make installation... [See More]
- Connector: DB9
- Network / Bus: PCI
- Serial Protocol: RS232
- Data Rate: 461
from Sealevel Systems, Inc.
The 7107 Low Profile PCI serial interface provides one serial port configurable for RS-422 or RS-485 and is capable of data rates to 921.6K bps. The 7107 utilizes an Oxford 16C950 UART to provide 128-byte Tx/Rx FIFOs, for maximum reliability in data intensive applications, and supports 9-bit... [See More]
- Connector: DB9
- Network / Bus: PCI
- Serial Protocol: RS232/422/485
- Data Rate: 922
from Sealevel Systems, Inc.
The 7205 PCI Low Profile serial interface provides two serial ports, each individually configurable for RS-232, RS-422 or RS-485. The board is capable of data rates to 921.6K bps and automatically handles RS-485 transmitter enable/disable. The 7205 utilizes 16C850 UARTs to provide 128-byte Tx/Rx... [See More]
- Connector: DB9
- Network / Bus: PCI
- Serial Protocol: RS232/422/485
- Data Rate: 922