Fanuc PC Daughter Board Module A20B-2900-0142 A2OB-29OO-O142 A20B29000142

A20B-2900-0142 | FANUC PMC-RA1 Control Module — I/O Link / SLC / Series 20/21 CNC Machine Sequence Controller

PMC — The Machine's Built-In PLC

Every FANUC CNC system incorporates a PMC (Programmable Machine Controller) — FANUC's embedded programmable logic controller that runs independently alongside the CNC's motion control. The PMC executes the machine sequence programme: the ladder logic that controls all non-cutting machine functions.

Without a functioning PMC:

• Coolant systems cannot be commanded on or off
• Hydraulic systems cannot sequence
• Tool changers cannot complete change cycles
• Door interlocks cannot be enforced
• Axis brakes cannot be released on demand
• Operator panel functions have no logic to respond to

The A20B-2900-0142 is the PMC module — the plug-in board that provides the PMC-RA1 controller within the Series 20/21 CNC. It is as essential to machine function as the CNC's motion control hardware.

Key Product Information

PMC-RA1 — Capability Level in the Series 20/21 PMC Family

The Series 20/21 CNC offered multiple PMC module options at different capability levels. The FANUC Series 20/21 Hardware Manual identifies the variants:

The RA1 designation identifies the PMC's capability level — programme step capacity, data register count, and instruction set. The RA3 variant (A20B-2901-0660) provides higher capability for more complex machine tools. The A20B-2900-0142 RA1 with I/O Link serves the standard Series 20/21 machine tool configuration.

Application Scenarios

Series 21 PMC module failure: A FANUC Series 21 CNC develops PMC alarms — the machine stops executing sequence functions, coolant and hydraulic commands fail to operate, and tool change cycles cannot complete. The A20B-2900-0142 PMC module is identified as the fault. Replacement restores PMC ladder execution and all machine sequence functions.

PMC module preventive replacement: A high-duty-cycle Series 20/21 machine running multiple production shifts undergoes a planned control unit refresh. The A20B-2900-0142 is replaced alongside memory modules as part of a comprehensive electronics renewal.

FAQ

Q1: What happens if the A20B-2900-0142 is replaced with A20B-2901-0660 (RA3 variant)?

The RA3 module (A20B-2901-0660) provides higher PMC capacity than the RA1. Fitting an RA3 module in a system designed for RA1 is physically possible if the module slot is compatible, but the CNC system software must support the RA3 PMC type. If the CNC's FROM-resident software does not support RA3, the PMC will not function correctly. Do not substitute PMC module variants without confirming software compatibility from the FANUC maintenance documentation.

Q2: Does replacing A20B-2900-0142 erase the machine's PMC ladder programme?

The PMC-RA1 module itself carries the PMC ladder programme in its onboard memory. Replacing the module means the new module starts with no ladder programme — the machine's specific PMC sequence logic must be reloaded from backup after fitting the replacement. This is why PMC ladder programme backup is as critical as CNC parameter backup before any PMC module maintenance.

Q3: What is the I/O Link scan cycle time on the A20B-2900-0142?

The I/O Link scan cycle — the time for the PMC to update all I/O Link connected I/O nodes — depends on the number of nodes connected and the PMC scan period. For the Series 20/21 with PMC-RA1, the I/O Link cycle is typically in the low millisecond range (1–3ms per full scan). This is sufficient for machine sequence control; time-critical safety circuits should always use hardwired signals rather than I/O Link for their primary protection path.

Q4: Can the A20B-2900-0142 be used if the Series 20/21 CNC has no I/O Link devices connected?

Yes. The I/O Link capability on A20B-2900-0142 is an available feature — it does not need to be used if the machine has no I/O Link devices. The PMC-RA1 functions normally with I/O Link devices absent. If the machine requires I/O Link at a later point (for example, a distributed operator panel upgrade), the I/O Link bus is available on the A20B-2900-0142 without requiring a module change.

Q5: What PMC-RA1 programme capacity does A20B-2900-0142 support?

The PMC-RA1 (RA1 = first capability level in the RA series) provides a defined maximum number of ladder programme steps, typically in the range of 1,000 to 3,000 steps depending on the Series 20/21 model and software version. The D (data), K (keep relay), and T (timer) register capacities are similarly defined for the RA1 level. For machines requiring more complex sequence programmes — approaching the RA1 step limit — the RA3 module (A20B-2901-0660) provides increased capacity.