Current hardware · V4.2 · RX/TX selectable

PiBot RJ12 Adapter V4.2

A protected RJ12/UART entry point for PiBot V4.96 Pro and V4.7B. Connect a Pendant directly, or place the adapter before an I/O Expander V5. The new board adds a physical RX/TX selection jumper.

V4.96 ProV4.7BPendant V4.2I/O Expander V5Physical RX/TX swap
V4.96 Pro connected to PiBot Pendant V4.2 through RJ12 Adapter V4.2
V4.96 Pro → RJ12 Adapter V4.2 → Pendant V4.2
Power off before moving a jumper or plugging an RJ12 cable. Remove controller USB and main power. If a battery is fitted in a Pendant, move its side switch down so the 18650 cell is electrically disconnected before inserting RJ12.

Section 1What changed in V4.2?

Selectable RX/TX

The V4.2 adapter adds a physical jumper group that can keep or exchange the two UART signal lines. This avoids modifying a verified cable when the two ends use the opposite RX/TX order.

For PiBot 4.x boards

This page documents the adapter with V4.96 Pro and V4.7B. V5.88 Ultra and V5.77 Carrier have their own direct RJ12 connection path and normally do not use this adapter there.

Protected interface

The adapter retains its series resistors and suppression components. It is an interface for the documented PiBot UART/RJ12 route, not a universal pinout converter.

Section 2Choose the connection path

Direct Pendant connection

Use the shortest path when only the Pendant needs the controller UART.

V4.96 / V4.7B→RJ12 Adapter V4.2→Approved RJ12 cable→Pendant V4.2

Connection through I/O Expander V5

Use this route when the Pendant is attached to the Expander's Pendant-side port.

V4.96 / V4.7B→Adapter V4.2→Expander V5→Pendant
The adapter is the controller-side entry point for these two 4.x boards. The I/O Expander adds I/O and provides a downstream Pendant connection; it does not remove the need for the correct controller-to-Expander UART wiring.

Section 3RX/TX selection — make one correction only

UART communication needs the transmitting line at one end to reach the receiving line at the other. The V4.2 adapter gives you a physical way to correct the route, but the same correction may also exist elsewhere in a current setup.

Correction pointAvailable onWhen to use itImportant
Physical RJ12 AdapterAdapter V4.2Correct the controller-side RX/TX route.Use the jumper group shown for the actual controller diagram below.
Physical PendantPendant V4.2Correct the Pendant-side RX/TX route.Do not also swap at the adapter.
Physical ExpanderI/O Expander V5Correct its controller-side or Pendant-side UART path.Treat each UART path separately; follow the V5 guide.
Software ESP3DCurrent ESP3D firmwareSettings → Setting Editor → Swap RX TXLeave physical hardware unswapped if software performs the correction.
Two swaps cancel each other. Choose exactly one correction point on one UART path. Never move power or ground positions: only the verified RX and TX signal route may be exchanged.

V4.96 Pro diagram

The verified V4.96 drawing marks the adapter selection group on the left side of the module. Copy the red-box position from the V4.96 image, not from the V4.7B image.

V4.7B diagram

The verified V4.7B drawing marks the adapter selection group on the right side. This difference is intentional because the controller-side header order is different.

Section 4Direct connection to Pendant V4.2

V4.96 Pro direct RJ12 wiring through Adapter V4.2 to Pendant V4.2
V4.96 Pro → Adapter V4.2 → Pendant V4.2Use the red-box adapter jumper position shown here. The documented UART2 route is TX GPIO.27 and RX GPIO.25; use the V4.96 configuration and RJ12 test page.
V4.7B direct RJ12 wiring through Adapter V4.2 to Pendant V4.2
V4.7B → Adapter V4.2 → Pendant V4.2Use the different red-box adapter jumper position shown here. The corrected V4.7B UART2 route is TX GPIO.27 and RX GPIO.25; use the V4.7B configuration and test page.
Do not copy the adapter jumper from the other controller image. V4.96 and V4.7B deliberately show different red-box positions. Always follow the picture for the board in front of you.

Section 5Connection through I/O Expander V5

The Expander sits between the controller-side adapter and the Pendant. It has its own RX/TX selection points, so check the complete signal path before changing anything.

V4.96 Pro connected through RJ12 Adapter V4.2 and I/O Expander V5 to Pendant
V4.96 Pro → Adapter V4.2 → Expander V5 → PendantFollow the red boxes on both the adapter and Expander. Use the Expander's From FluidNC Mainboard port for the controller-side cable.
V4.7B connected through RJ12 Adapter V4.2 and I/O Expander V5 to Pendant
V4.7B → Adapter V4.2 → Expander V5 → PendantUse the V4.7B-specific adapter position. The Expander-to-Pendant route is checked separately from the controller-to-Expander route.
Count corrections per UART path. If the adapter performs the controller-side swap, do not repeat that same correction at the Expander input. If the Pendant-side route needs a swap, use one Pendant-side point only.

Section 6First power-up and communication check

Before power

Confirm the controller model and use only its matching diagram.
Check every jumper is firmly seated and only one RX/TX correction is active on each UART path.
Use a verified PiBot RJ12 cable. A plug that mechanically fits does not prove the power, ground and UART pinout is compatible.
Disconnect the Pendant battery, then connect cables while controller USB and main power are off.

Communication test

Power the controller and open the correct FluidNC console or interface.
Confirm the board-specific UART configuration is enabled. On V4.96 and V4.7B, OLED and RJ12 UART2 share GPIO.27/25 and cannot be enabled together.
Verify that keys, display/status data or Expander communication work reliably before enabling machine motion.
Power down again before changing any jumper, cable or downstream module.

Pass

The Pendant or Expander powers normally, establishes communication and remains stable. Buttons/status respond as expected with no reset loop or unusual heat.

Fail — stop here

If the unit powers but cannot communicate, resets, becomes hot or behaves intermittently, remove power. Do not keep trying jumper combinations while energized.

Section 7Troubleshooting and related guides

Powered, but no communication

  • Check for two active RX/TX swaps that cancel each other.
  • Confirm you used the V4.96 or V4.7B adapter group shown in the matching diagram.
  • If ESP3D software swap is active, return the physical route to the unswapped position.
  • Confirm the correct UART pins, baud rate and OLED sharing rule on the controller page.
  • With an Expander, confirm the controller cable enters From FluidNC Mainboard.

Unstable or intermittent link

  • Use the approved cable and keep it away from motor, spindle and VFD wiring.
  • Check RJ12 plugs latch fully and jumpers are not loose or offset by one pin.
  • Do not hot-plug the adapter, cable, Expander or Pendant.
  • If any board becomes unusually hot, remove power and re-check the complete pinout before reuse.
Pendant V4.2 guide I/O Expander V5 guide Shared RX/TX FAQ V4.96 RJ12 test V4.7B RJ12 test

Legacy overview drawings

These original drawings are kept for existing users and earlier hardware. For the Adapter V4.2 RX/TX jumper position, the four current diagrams above take precedence.

Legacy direct RJ12 connection overview
Legacy direct connection overviewReference for earlier RJ12 adapter installations.
Legacy RJ12 connection through I/O Expander overview
Legacy Expander connection overviewReference for earlier I/O Expander installations.
This guide covers PiBot RJ12 Adapter V4.2 with V4.96 Pro and V4.7B, used either directly with a Pendant or before I/O Expander V5. Controller GPIO assignments and configuration files remain controller-specific.