Fanuc Module A20B-2901-0340 A20B29010340 A2OB-29O1-O34O

A20B-2901-0340 | FANUC Type A Servo Interface Control Module — Daughter Board / Type A Bus Interface / CNC Servo Drive Systems

What Is the Type A Servo Interface?

In FANUC's servo communication history, the Type A interface represents the serial servo bus protocol used on CNC generations that predate FSSB (Fibre Servo Serial Bus). Where FSSB uses optical fibre for completely noise-immune servo communication, the Type A interface uses dedicated serial cables between the CNC and the servo drive amplifiers.

The A20B-2901-0340 is the plug-in daughter board that implements this Type A interface in the CNC. It sits on the CNC's main board or in a defined module slot and provides the physical and logical Type A bus connection between the CNC's servo interpolation processor and the connected servo drives.

Key Product Information

Daughter Board — The Interface Layer

The A20B-2901-0340 is a daughter board: a secondary PCB that plugs into a dedicated socket on the CNC's main board or host board. It does not replace the main board — it adds a specific interface function to it.

In the Type A servo architecture:

The CNC main board performs servo interpolation — calculating the position command increments for each axis every servo cycle.

The A20B-2901-0340 daughter board translates these position commands into the Type A serial data stream and transmits them to the servo drives. Simultaneously, it receives the encoder feedback data returning from the drives and passes it to the main board's servo calculation.

The Type A servo drives (such as A06B-6058 and A06B-6079-H204 series) receive the commands and return feedback on the same Type A serial cables.

When the A20B-2901-0340 fails, the CNC loses communication with the servo drives — axis servo alarms are generated and all axis motion is inhibited.

Application Scenarios

Type A servo communication failure: A FANUC CNC generates servo alarms on all Type A interface axes simultaneously, with no individual axis fault. The servo drives and motors test correctly. The A20B-2901-0340 daughter board is identified as the fault. Replacement restores servo communication.

Planned module replacement: A facility maintaining older FANUC CNC systems with Type A servo interface replaces the A20B-2901-0340 proactively during a scheduled maintenance period, ahead of potential age-related failure.

FAQ

Q1: What CNC systems use the A20B-2901-0340 Type A servo module?

The Type A servo interface was used in FANUC CNC generations that predate the FSSB era — including various Series 0, Series 16, Series 18 Model A/B/C variants, and others equipped with Type A servo drives. The specific CNC models compatible with A20B-2901-0340 depend on which main board slot this daughter board is designed to fit. Confirm from the CNC's spare parts list.

Q2: Can the A20B-2901-0340 be used with FSSB servo drives?

No. The Type A serial bus protocol is incompatible with FSSB (Fanuc Servo Serial Bus, fibre optic). FSSB drives require an FSSB servo card (such as the A20B-3300-0033 described elsewhere in this series). The A20B-2901-0340 serves Type A interface drives only. Fitting a Type A servo module in a system with FSSB drives will not establish servo communication.

Q3: Does replacing A20B-2901-0340 require servo parameter adjustment?

Servo axis parameters (motor ID, encoder type, gain values, current limits) are stored in the CNC's main parameter memory — not in the servo interface daughter board. Replacing A20B-2901-0340 does not affect stored servo parameters. After fitting the replacement, the CNC re-establishes Type A servo communication and applies the existing parameters. Verify servo readiness and run low-speed tests before full production.

Q4: What are the Type A interface cable requirements for this module?

The Type A servo interface uses dedicated serial cables — typically FANUC-specified shielded cables running from the servo module's output connector on the CNC to each connected servo amplifier's servo interface input. Cable routing, shielding, and connector integrity all affect Type A communication reliability. When the A20B-2901-0340 is suspected faulty, inspect the Type A cables and connectors as part of the fault diagnostic process before concluding the board has failed.