Description
The A20B-3900-0165 is a memory module used inside FANUC CNC controller systems. It combines non-volatile Flash ROM (FROM) and battery-backed Static RAM (SRAM) on a small circuit card that plugs into the controller’s main electronics board to store essential firmware and system data.
Key Characteristics:
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💾 Memory Type: FROM + SRAM module — 32 MB Flash ROM plus 3 MB SRAM.
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🧠 Function:
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The FROM portion holds the controller’s core firmware and system programs that the CNC needs to boot and operate.
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The SRAM portion holds runtime data and machine parameters, often backed by battery power so settings aren’t lost when the controller is powered down.
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🔌 Installation: Plugs into a designated memory socket on the controller’s main PCB or memory backplane.
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🛠️ Use: Commonly found in FANUC i-Series “B” controllers such as 16i-B, 18i-B, and 21i-B, where FROM/SRAM modules are required as part of the system’s core electronics.
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📦 Status: This part is typically discontinued by FANUC but remains widely available through aftermarket suppliers as new surplus, refurbished, or tested units.
🧩 Practical Notes
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Without a working memory module like this, a FANUC controller may fail to initialize, lose saved parameters, or be unable to run properly because it lacks essential firmware and data.
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When replacing this module, it’s important to restore machine parameters and backups after installation so the controller retains correct configuration and programs.