PCIe 4-port RS232 Serial Adapter Card StarTech PEX4S953LP — 16950 UART, 256B FIFO, Low Profile

The StarTech PEX4S953LP is a PCIe 4-port RS232 serial adapter card that adds four DB9 serial ports to a desktop or server via a PCI Express slot. It uses the Asix AX99100 chipset with an industry-standard 16950 UART and 256-byte FIFO buffers, and supports baud rates up to 921.6 Kbit/s. The card is PCI Express 1.1 compliant, supplied with low-profile and optional full-profile brackets for installation in different chassis, and is CE/FCC certified with an MTBF of 214,358 hours. Drivers are available for Windows and supported Windows Server versions; Linux compatibility is also indicated.

Advantages

The adapter provides four independent RS232 (DB9) ports on a single PCIe card, enabling high-speed serial communication up to 921.6 Kbit/s. Built on a 16950 UART with 256-byte FIFO per transmitter and receiver, it reduces CPU interrupts and improves data throughput for multiple simultaneous serial connections. The low-profile form factor and included full-profile bracket simplify installation in a range of systems. Compliance with PCIe 1.1 and CE/FCC certification ensure reliable interoperability and regulatory compliance.

Suitable for

• Connecting legacy serial devices such as receipt printers, barcode scanners, and industrial controllers
• Integrating point-of-sale terminals, PIN pads, and card readers that require RS232 interfaces
• Managing serial communications for network equipment, modems, and laboratory instruments
• Expanding serial port capacity in servers and workstations with limited onboard COM ports

Key specifications

• Interface: PCI Express (PCIe) 1.1 host interface
• Serial ports: 4 × RS232 DB9 connectors
• Chipset: Asix AX99100
• UART: Industry-standard 16950
• FIFO: 256-byte FIFO per transmitter and receiver
• Maximum baud rate: Up to 921.6 Kbit/s
• Form factor: Low-profile card (includes full-profile bracket)
• Power output: 5/12V on Pin 9 when external power is connected
• Certifications: CE, FCC
• MTBF: 214,358 hours

How to use

Power down the computer and insert the card into an available PCIe slot, choosing the low-profile or full-profile bracket as appropriate for your chassis. Secure the bracket, reconnect power, and boot the system. Install the appropriate drivers for your operating system (Windows, supported Windows Server versions, or Linux) following the vendor instructions. Connect serial devices to the DB9 ports and configure port settings (baud rate, data bits, parity, stop bits) in your OS or serial communication software to match the connected devices. If external power is required for pin 9 output, connect the external power source as specified by your device documentation.

Usage recommendations

Use shielded serial cables to minimize interference and verify baud rate and handshake settings for each connected device. For stable multi-device communication, enable the card's FIFO buffering and match serial parameters to the peripheral's requirements; consult device manuals for recommended power connections if using the 5/12V output on pin 9.