AST 5251/11 Enhanced Twinax Emulator ISA Card 202139-002 Rev X4 IBM AS/400

AST 5251/11 Enhanced Twinax Emulator ISA Card 202139-002 Rev X4 IBM AS/400

The AST 5251/11 is an 8-bit ISA expansion card that enables a DOS-based PC to emulate an IBM 5251 twinax terminal, allowing the host machine to communicate directly with IBM AS/400, System/36, and System/38 midrange systems over a twinax cable network. The board is labeled "Enhanced" and carries part number 202139-002 at hardware revision X4, visible on the label affixed to the PCB.

Specifications & What's Included

• Manufacturer: AST
• Model: 5251/11 Enhanced
• Part Number (MPN): 202139-002
• Hardware Revision: Rev X4
• Bus Interface: 8-bit ISA (full-length card)
• Protocol / Emulation: IBM 5250 twinax terminal emulation
• Bracket Connector: DB-15 twinax port with TERM / THRU selector switch on bracket
• On-board ICs visible: MC74F08N logic ICs (multiple), Kappa-Taiwan IC, additional TTL logic array
• Board finish: green PCB, full-length ISA form factor
• Included: card only — no cables, software, or AST 5251/11 was designed for the 1980s and early 1990s PC-to-IBM-midrange connectivity market. IBM's AS/400 (introduced 1988), System/36, and System/38 used a proprietary twinax cabling scheme — a two-wire, multi-drop network that connected up to seven terminals or workstations to a single port on the host. Rather than use a dedicated IBM 5251 or 5291 display station, businesses could install a twinax emulator card like the AST 5251/11 into an ISA-bus PC and run emulation software, giving the PC full 5250 terminal functionality at a lower cost and with the added flexibility of a general-purpose computer. The TERM/THRU selector on the bracket allowed the card to be placed anywhere in the daisy-chain: TERM terminated the cable at the last device, while THRU passed the signal down to the next station. AST Research was one of several third-party vendors — alongside Arlan, Attachmate, and IBM itself — producing these cards during the height of IBM midrange installations in corporate environments. Today these cards are sought by collectors and by organizations still maintaining legacy AS/400 or System/36 infrastructure.
  Condition: Used
  This AST 5251/11 Enhanced Twinax Emulator ISA card (202139-002 Rev X4) has been inspected and appears to be in good used condition. The board looks clean overall with no visible cracked traces, burned components, or physical damage. The bracket and DB-15 twinax connector appear intact, and the ISA edge connector contacts look serviceable. Normal light surface aging is consistent with the card's age and prior use. Please view our photo set and contact us if you have any questions. Please note: We have multiple units in stock — yours may not be the one shown in the photos, however, it will be similar in condition and function. Visit Our Store

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