StarTech PEX2S953LP 2-Port Low-Profile PCIe RS232 Serial Controller Card

Overview

The StarTech PEX2S953LP is a low-profile PCIe x1 serial controller card that adds two RS232 DB-9 ports to any desktop or 1U/2U rackmount server where native COM ports are absent or exhausted. Built around the Asix AX99100 chipset, it supports baud rates up to 921.6 Kbps and fits slim-chassis systems that cannot accept standard-height expansion cards. If you are integrating legacy serial devices — access control panels, DVRs, PTZ camera controllers, serial matrix switches, or industrial PLCs — into a modern server platform that shipped without COM ports, this card closes that gap without requiring a full-height slot or an external USB-to-serial adapter.

The card measures just 4.4 × 3.1 inches in the bracket plane and 0.9 inches wide, making it a practical fit in compact workstations and short-depth rackmount servers. It draws power directly from the PCIe slot and optionally from an LP4 internal power connector, with pin 9 on each DB-9 port selectable between 5V and 12V — useful when powering serial devices that draw auxiliary voltage over the connector.

Key Features

• Asix AX99100 Chipset: a mature, well-supported controller with stable driver availability across Windows 7 through 11, Windows Server 2003 through 2022, and Linux kernel 2.4 and later. Wide OS coverage means you are not locked out of a deployment if the host runs an older server OS or a Linux-based NVR appliance.
• 921.6 Kbps Maximum Baud Rate: nearly double the 460.8 Kbps ceiling of standard 16550-based cards. That headroom matters for high-throughput serial protocols used in industrial automation, serial-over-IP bridges, and certain DVR/NVR control buses where lower baud rates create command latency.
• 256-Byte FIFO per Port: the larger FIFO buffer reduces CPU interrupt load compared to the 16-byte FIFO on legacy 16550 UARTs. On a busy server running multiple serial data streams, fewer interrupts means lower overhead — relevant if this card shares the host with a running VMS or database.
• Low-Profile Card Format: at 3.1 inches tall, the PEX2S953LP fits 1U and 2U rackmount chassis as well as compact mini-tower workstations that use low-profile slots. Full-height brackets are not the default — confirm your chassis slot height before ordering if you need the standard bracket.
• Selectable 5V/12V on DB-9 Pin 9: some PTZ camera receivers and serial-controlled devices draw power or a logic reference from pin 9. The ability to select between 5V and 12V via jumper means you can match the device requirement without an external voltage injector.
• PCIe 1.1 x1 Interface: uses a single PCIe lane, compatible with any x1, x4, x8, or x16 physical slot running PCIe 1.1 or later. Serial throughput is nowhere near PCIe bandwidth limits, so the 1.1 spec is not a constraint — and this compatibility means the card drops into virtually any modern motherboard.
• Flexible Flow Control: supports hardware RTS/CTS, software XON/XOFF, and no flow control. Match the setting to whatever the attached serial device expects — mismatched flow control is a common source of dropped characters in surveillance and access control integrations.
• Full Data Configuration Range: 5, 6, 7, or 8 data bits (plus 9-bit mode), parity options including None/Odd/Even/Space/Mark, and stop bits of 1, 1.5, or 2 cover every RS232 framing variant you are likely to encounter in field equipment.
• Operating Temperature -10°C to 80°C: the extended upper limit means this card handles the elevated ambient temperatures inside a running server chassis without throttling or instability — relevant in poorly cooled IDF closets or edge-deployed workstations.
• Internal LP4 Power Connector: the optional LP4 connection provides supplemental power to pin 9 voltage output. If your host chassis has an LP4 header available, using it ensures stable auxiliary voltage delivery to attached serial devices even under load.

Integration & Compatibility

The PEX2S953LP integrates directly with StarTech expansion cards and adapters and fits within broader PCIe serial controller card deployments. In security and surveillance contexts, the card pairs with access control panels that use RS232 for host communication, and with DVR/NVR platforms requiring a dedicated COM port for PTZ control buses. Refer to your serial integration planning guide when migrating legacy serial-controlled devices onto a modern IP-based infrastructure — knowing which devices still require physical COM ports versus those that can shift to serial-over-IP determines how many ports you actually need. The card occupies a single PCIe x1 slot and presents as two standard COM ports under Windows Device Manager, requiring no special application-layer configuration beyond driver installation.

Frequently Asked Questions

Q: Is the PEX2S953LP compatible with Windows Server 2019 and 2022?

A: Yes. The Asix AX99100 chipset driver supports Windows Server 2003 through 2022, including Server 2019 and 2022.

Q: What is the maximum baud rate the PEX2S953LP supports?

A: 921.6 Kbps per port — roughly double what standard 16550-based cards offer, which helps with high-throughput serial protocols used in industrial and security applications.

Q: Does the PEX2S953LP fit in a 1U rackmount server?

A: Yes. The card is low-profile at 3.1 inches tall, designed for 1U and 2U chassis and compact workstations that use low-profile PCIe slots.

Q: What does the selectable 5V/12V on pin 9 mean in practice?

A: Some serial devices, including certain PTZ camera receivers and industrial controllers, draw an auxiliary voltage from DB-9 pin 9. The jumper lets you match 5V or 12V to the device's requirement without an external power injector. The LP4 connector must be used to enable pin 9 voltage output.

Q: Does the PEX2S953LP work with Linux?

A: Yes. Driver support covers Linux kernel 2.4 and later, making it compatible with Linux-based NVR appliances, Ubuntu/Debian servers, and most embedded Linux platforms running current or recent kernels.

Q: Can the PEX2S953LP be installed in a full-height PCIe slot?

A: The card is physically low-profile. It will seat in a full-height x1, x4, x8, or x16 PCIe slot electrically, but you would need a standard-height bracket to secure it properly — confirm bracket availability if your chassis requires one.

James Everett

The detail I keep coming back to on the PEX2S953LP is the 256-byte FIFO — it sounds minor, but on a server running a VMS alongside a serial PTZ control bus, the reduced interrupt rate compared to a legacy 16550 UART actually keeps CPU utilization measurably flatter during burst serial traffic. That matters when the same machine is also encoding video.

Technical Highlights:

• 921.6 Kbps Baud Rate: at nearly double the ceiling of a standard 16550 card, this headroom prevents baud-rate bottlenecks when integrating serial matrix switchers or high-speed industrial PLC communications alongside standard 9600/115200 bps device control.
• AX99100 Chipset: broad driver support from Windows 7 through Server 2022 and Linux 2.4+ means you are not chasing driver compatibility six years into a deployment when an OS update lands.
• Pin 9 Voltage Selection (5V/12V): the jumper-selectable auxiliary voltage on DB-9 pin 9, backed by the LP4 internal connector, eliminates the need for a separate inline power injector when the attached serial device draws auxiliary power from the port — a common requirement on older PTZ receivers.

Deployment Considerations:

• The LP4 connector is required to supply voltage on pin 9. If the host chassis has no LP4 header available — common in newer all-modular PSU designs — you will need an LP4 adapter or an alternate power source before relying on pin 9 power for attached devices.
• The card ships in low-profile form. If the destination chassis is full-height only, verify that a standard-height bracket is available before committing to this SKU — installing without the correct bracket leaves the card unsecured in the slot.

This card earns its place in compact rackmount NVR builds and edge security servers where a 1U chassis needs COM port access for legacy PTZ control or serial-connected access control hardware, and where USB-to-serial adapters introduce driver instability or interrupt the clean cable management the rack requires.