FANUC Board A20B-3900-0163 A20B39000163 A2OB-39OO-O163

FANUC A20B-3900-0163 | 32MB FROM + 1MB SRAM Memory Module — Series 16i / 18i / 21i Model A

Larger Memory for More Complex 16i/18i/21i Configurations

The A20B-3900-0163 is the 32MB FROM + 1MB SRAM variant in FANUC's A20B-3900 plug-in memory module family for i-Series CNC controllers. It plugs into the main master PCB alongside the CPU module, graphics board, FSSB board, and other memory-related boards that collectively define the 16i/18i/21i Model A controller's capability.

The larger 32MB FROM capacity — twice the size of the A20B-3900-0160 (16MB FROM + 1MB SRAM) — serves 16i/18i/21i installations with more complex control configurations: larger PMC ladder programs, additional CNC software options, machine builder custom applications that need more flash storage than the smaller module provides. If the installed machine uses the 32MB variant, it is because the software installed on that control requires that capacity to run.

FROM (Flash ROM — 32MB, non-volatile): Stores the CNC operating system, PMC ladder program, machine builder software, and software option data. Flash retains data without power or battery. At power-on, the CNC loads its operating software from the FROM module. A corrupted or failed FROM module prevents the CNC from starting — typically presenting as a checksum alarm or boot failure at power-on.

SRAM (1MB — battery-backed): Stores CNC parameters, tool offset tables, work coordinate offsets, and part programs. The backup battery (in the CNC chassis, not in this module) maintains SRAM content through power cycles. When the battery depletes, SRAM content is lost.

Key Specifications

Not the Same as A20B-3900-0160

These are different modules. The 32MB FROM on the -0163 is not interchangeable with the 16MB on the -0160 — software images written for a 32MB module will not fit in a 16MB module. Always confirm the installed module's exact part number from its label.

FAQ

Q1: What does the 32MB FROM store, and why does it matter for replacement?

The FROM stores the CNC operating system, PMC ladder program, machine builder software, and CNC option data. A replacement module arrives blank — all of this must be rewritten from a backup before the machine can run. The 32MB capacity means the installed control requires this larger module; the 16MB A20B-3900-0160 does not hold the same software image and cannot substitute.

Q2: Is the A20B-3900-0163 the same as A20B-3900-0160?

No. They are different modules — 32MB vs 16MB FROM capacity. A software image built for 32MB does not fit in a 16MB module. Confirm the exact part number from the installed module's label before ordering a replacement.

Q3: What must be done before removing the A20B-3900-0163?

Back up all CNC data — parameters, PMC ladder, tool offsets, work coordinates, part programs — before removing the module. The replacement arrives blank and requires data restoration after installation. The backup is what determines whether recovery takes minutes or days.

Q4: Where is the backup battery for the SRAM, and when does it need replacing?

The SRAM backup battery is in the CNC chassis, not in this module. FANUC CNC systems generate a low-battery alarm before the battery reaches the critical voltage threshold. Replace the battery with the CNC powered on to maintain SRAM content during the change. A fully depleted battery causes complete SRAM data loss — parameters and programs must be reloaded from backup.

Q5: The installed A20B-3900-0163 is at revision /02A. Is /01A compatible as a replacement?

Minor hardware revision suffixes within the same base part number typically represent PCB layout changes or component updates that maintain the same functional specification. In most cases later revisions are backward-compatible with earlier revision installations. Confirm with the machine's maintenance documentation or a FANUC service resource if uncertainty exists for the specific application.