This article covers StarTech.com シリアル増設カード.

Overview

The StarTech.com PEX2S953 is a 2-port RS232C serial expansion card designed to bring legacy COM port connectivity to modern desktop PCs and servers. Powered by the ASIX AX99100 controller with 16950 UART, each port delivers bidirectional communication at up to 921.6 Kbps, along with a 256-byte FIFO buffer and support for 9-bit data framing often required in industrial automation. As the direct upgrade to the popular PEX2S952, this card addresses the growing need for reliable serial interfaces on motherboards that have long abandoned built-in COM ports. It ships with both standard and low-profile brackets, making it suitable for full-size towers, slim desktops, and rack-mount servers alike. The ability to independently configure pin-9 power (12V/5V/off) per port adds extra flexibility for powering external serial devices without separate adapters.

Connectivity & Compatibility

The PEX2S953 uses a PCI Express 2.0 x1 interface, requiring only an available x1 or larger slot. Operating system support covers Windows 10/11/Server and Linux (in-kernel drivers). Pin-9 power options (12V/5V/none) are configurable per port for devices that need bus-powered signaling. Two low-profile brackets are included in the package, allowing installation in 1U chassis without extra hardware. The card is fully backward compatible with PCIe 3.0/4.0/5.0 slots, though it operates at x1 Gen 2 speeds.

Product Info

Released around 2020, the PEX2S953 has established itself as a reliable workhorse in the serial expansion card market. The typical street price is approximately $55–60 USD (around ¥7,500 JPY on). While slightly more expensive than budget cards using CH340-based chips, the AX99100 offers superior driver maturity, broader OS support, and manufacturer-backed lifetime technical support. It occupies the mid-range tier, balancing cost with industrial-grade reliability.

Best Use Cases

Industrial automation engineers working with PLCs, CNCs, and scientific sensors will appreciate the 921.6 Kbps speed and 256-byte FIFO buffer for handling larger data transfers without overruns. POS/retail system integrators benefit from the separate pin-9 power configuration, simplifying wiring for receipt printers and barcode scanners that require powered serial ports. DIY enthusiasts who need to connect legacy peripherals such as serial mice, joysticks, or MIDI interfaces to modern builds will find this card an easy, driver-friendly solution.

Things to Consider

While the card is recognized by standard OS inbox drivers, advanced features like 9-bit data mode require the manufacturer's dedicated driver package. macOS is not officially supported, so Mac users should look for alternative Thunderbolt-to-serial adapters. The PCIe 2.0 x1 bandwidth is sufficient for legacy serial speeds, but the card won't benefit from being installed in a faster slot. Finally, for single-port needs, the PEX2S952 (the previous model) may be a more cost-effective choice if 9-bit support is not required.

Product Disclosure (Amazon)

  • Manufacturer: StarTech.com(スターテック)
  • Seller: Startech Japan KK
  • Fulfilled by: Amazon
  • ASIN: B085QMN3HD
  • Note: This article covers a manufacturer-made product based on Amazon listing details.